simon riesen the usage of mainstream technologies for public

Helsinki University of Technology

Department of Electrical and Communications Engineering

Simon Riesen

The usage of mainstream technologies for public safety and

security networks

Thesis submitted in partial fulfilment of the requirements for the degree

of Master of Science in Engineering.

Espoo, Finland, October 9, 2003

Supervisor: Professor Raimo Kantola

Instructor: Jaakko Saijonmaa, Dr. Tech.

Helsinki University of Technology Abstract of the Master’s Thesis

Author: Simon Riesen

Name of the Thesis: The usage of mainstream technologies for public safety and

security networks

Date: October 9, 2003 Number of pages: 64

Department: Department of Electrical and Communications Engineering

Professorship: S-38 Telecommunications Management

Supervisor: Professor Raimo Kantola

Instructor: Jaakko Saijonmaa, Dr. Tech.

The two ETSI-standardized technologies TETRA and GSM with ASCI functionalities

have been compared using an analytic hierarchical process consisting of a technical

and an economic comparison. The study focuses on the functionality of group calls,

which is one of the most important requirements for public safety and security (PSS)

networks. The technical analysis is based on the air interface specifications and points

out whether certain functionalities are supported or not. Capacity requirements have

been calculated based on a typical user profile and a countrywide network for

Germany. The economic analysis takes into account the network’s CAPEX, OPEX and

the technology risk of each solution. In the case of GSM, the services could be offered

based on an existing network platform and, therefore, major savings in the network

costs could be expected.

However, TETRA appears to have clearly better performance, not only on the

technical, but also on the economic level. The main reasons for this conclusion are the

non-existence of shifting area group calls, long call set-up times and the relatively small

cell sizes for GSM. The combination of these restrictions result in significantly higher

network capacity requirements for GSM compared to similar TETRA solutions. The

additional capacities have direct impact on the network costs. Currently, the TETRA

standard offers the most economic and reliable group call services for customers with

hardly predictable moving behaviour like PSS users.

Keywords: TETRA, GSM ASCI, group communication, network costs

Teknillinen Korkeakoulu Diplomityön Tiivistelmä

Tekijä: Simon Riesen

Työn nimi: Mainstream-teknologioiden käyttö viranomaisverkoissa

Päivämäärä: 9.10.2003 Sivumäärä: 64

Osasto: Sähkö- ja tietoliikennetekniikan osasto

Professuuri: S-38 Telecommunications Management

Työn valvoja: Professori Raimo Kantola

Työn ohjaaja: TkT Jaakko Saijonmaa

Työssä vertaillaan kahta ETSI-standardisoitua teknologiaa, TETRAa ja ASCI-

toiminallista GSM-teknologiaa, käyttäen analyyttista hierarkkista prosessia, johon

sisältyy sekä tekninen että taloudellinen vertailu. Työ keskittyy ryhmäpuhelutoimintaan,

joka on yksi tärkeimmistä viranomaisverkkojen edellytyksistä. Tekninen analyysi

perustuu ilmatiespesifikaatioon ja tarkastelee, tukeeko teknologia tiettyjä toimintoja.

Kapasiteettivaatimukset on laskettu tyypilliselle käyttäjäprofiilille ja Saksan

maanlaajuiselle verkolle. Taloudellinen analyysi ottaa huomioon verkon CAPEX- ja

OPEX-kustannukset sekä kunkin sovelluksen teknologiariskin.

GSM-verkkoa käytettäessä hyödynnetään jo olemassa olevaa verkkoinfrastruktuuria,

minkä oletettiin mahdollistavan suuret kustannussäästöt. TETRA näyttää kuitenkin

olevan parempi ratkaisu sekä teknisesti että taloudellisesti. Tätä johtopäätöstä tukee

GSM:n ryhmäpuhelun pitkä muodostusaika, suhteellisen pienet solut ja se, että GSM ei

tue shifting area -ryhmäpuheluja. Näiden rajoitusten seurauksena GSM:n

kapasiteettivaatimukset ovat selvästi korkeammat kuin vastaavassa TETRA-verkossa.

Lisäkapasiteetit vaikuttavat suoraan verkon kustannuksiin. Tällä hetkellä TETRA-

standardi tarjoaa taloudellisimmat ja luetettavimmat ryhmäpuhelupalvelut asiakkaille,

joiden liikkumista on vaikea ennustaa.

Avainsanat: TETRA, GSM ASCI, ryhmäkommunikaatio, verkon kustannukset

ACKNOWLEDGEMENTS

I would like to thank Professor Raimo Kantola for his guidance and support during

writing of the thesis. I want to express my thanks to my instructor Jaakko Saijonmaa for

valuable comments, ideas and support.

Last, but most importantly, I would like to thank my friends and my study colleagues,

Tarja, Markku and Mika, for their support during the studies.

Espoo, October 9, 2003

Simon Riesen

of 64

TABLE OF CONTENTS

1. LIST OF ABBREVIATIONS .................................................................................... 3

2. INTRODUCTION ..................................................................................................... 5

2.1 RESEARCH PROBLEM AND OBJECTIVES ............................................................... 5

2.2 BACKGROUND.................................................................................................... 6

2.3 END-USER- REQUIREMENTS................................................................................ 7

2.3.1 Network functions ......................................................................................... 7

2.3.2 Network security ........................................................................................... 8

2.4 GROUP CALL RELATED FEATURE DESCRIPTIONS .................................................. 9

2.4.1 Push-to-talk functionality............................................................................... 9

2.4.2 Group call area ........................................................................................... 10

2.4.3 Dynamic group number allocation (DGNA)................................................. 10

2.4.4 Priorities...................................................................................................... 10

2.4.5 Late entry.................................................................................................... 11

2.4.6 Scanning and priority scanning................................................................... 11

2.4.7 Data calls (SDS and status)........................................................................ 11

2.5 AVAILABLE TECHNICAL SOLUTIONS.................................................................... 11

2.5.1 TETRA ........................................................................................................ 12

2.5.2 GSM ASCI .................................................................................................. 12

2.5.3 Tetrapol....................................................................................................... 13

3. EXISTING ANALYSIS........................................................................................... 14

3.1 NETWORK FUNCTIONS...................................................................................... 14

3.1.1 Group call memberships............................................................................. 14

3.1.2 Handover times........................................................................................... 15

3.1.3 Priorities...................................................................................................... 15

3.1.4 Data messages (SDS and status) .............................................................. 16

3.2 NETWORK CAPACITY ........................................................................................ 16

3.2.1 Coverage & Capacity.................................................................................. 16

3.2.2 Call set-up times ......................................................................................... 16

3.2.3 Group call area ........................................................................................... 17

3.3 NETWORK SECURITY ........................................................................................ 17

3.4 ECONOMIC ARGUMENTS ................................................................................... 18

3.4.1 Network infrastructure................................................................................. 18

3.4.2 Radio terminals........................................................................................... 19

3.4.3 Risk factors ................................................................................................. 19

of 64

3.5 SUMMARY OF LITERATURE REVIEW.................................................................... 20

4. HIERARCHICAL ANALYSIS ................................................................................ 22

4.1 AIR INTERFACE SPECIFICATIONS ....................................................................... 23

4.1.1 GSM ASCI .................................................................................................. 23

4.1.2 TETRA ........................................................................................................ 25

4.1.3 Comparison of specified features ............................................................... 26

4.2 TECHNICAL ANALYSIS ....................................................................................... 27

4.2.1 Network functions ....................................................................................... 27

4.2.2 Network capacity ........................................................................................ 29

4.2.3 Network security ......................................................................................... 40

4.2.4 Summary of comparison on technical level ................................................ 41

4.3 ECONOMIC ANALYSIS........................................................................................ 44

4.3.1 CAPEX........................................................................................................ 46

4.3.2 OPEX.......................................................................................................... 50

4.3.3 Risks ........................................................................................................... 52

4.3.4 Summary of comparison on economic level ............................................... 54

4.4 COMBINATION OF THE RESULTS ........................................................................ 58

4.5 SENSITIVITY ANALYSIS...................................................................................... 60

4.6 CONCLUSIONS ................................................................................................. 61

4.7 FUTURE PROSPECTS ........................................................................................ 62

5. LIST OF REFERENCES ....................................................................................... 63

of 64

1. LIST OF ABBREVIATIONS

AIE Air Interface Encryption

API Application Programming Interface

ASCI Advanced Speech Call Item

BSC Base Station Controller

BTS Base Transceiver Station

CAPEX CAPtial EXpenses

DGNA Dynamic Group Number Allocation

E2EE End-To-End Encryption

EADS European Aeronautic Defence and Space Company

eMLPP Enhanced Multi-Level Precedence and Pre-emption service

ETSI European Telecommunications Standardisation Institute

FDMA Frequency Division Multiple

FIFO First In First Out

IMPEX IMPlementation EXpenses

ISDN Integrated Services Digital Network

ITSI Individual TETRA Subscriber Identity

GCR Group Call Register

GoS Grade of Service

GSM Global System for Mobile communication

GTSI Group TETRA Subscriber Identity

HLR Home Location Register

MCCH Main Control CHannel

MS Mobile Subscriber

MSC Mobile Services Switching Centre

MSISDN Mobile Subscriber ISDN

NCH Notification CHannel

NPV Net Present Value

OPEX Operating EXpenses

PAS Public Available Specifications

of 64

PMR Professional Mobile Radio

PoC Push-to-talk over Cellular

PSS Public Safety and Security

PTT Push-To-Talk button

SDS Short Data Service

SIM Subscriber Identity Module, SIM Card

SMS Short Message Service

SwMI Switching and Management Infrastructure

TCH Traffic CHannel

TDMA Time Division Multiple Access

TEA2 TETRA Encryption Algorithm 2

TETRA Terrestrial Trunked mobile Radio

TETRA MoU TETRA Memorandum of Unterstanding

TIP TETRA Interoparability Profile

VBS Voice Broadcast Service

VGCS Voice Group Call Service

VIRVE Viranomaisverkko

VLR Visitor Locations Register

of 64

2. INTRODUCTION

Public safety and security (PSS) networks are dedicated radio communication systems

for police, fire brigades, ambulances and other related public services and

organisations. These so-called Professional Mobile Radio (PMR) networks are also

used by other user groups: military, public transport companies, energy and water

supply companies and so on. However, the user-requirements may vary between the

groups very much and this thesis will focus on PSS users only.

The main differences in the functionality compared to the existing public mobile

networks like GSM are group call functionalities. Very basic group calls do also exist on

a GSM basis; however, they do not offer the same flexibility and reliability as the ones

used in dedicated technologies like TETRA. Group calls are an essential part of PSS

networks and also form the main technical barrier for public mobile networks to enter

this market. Therefore, this thesis will focus on group calls and the implications for

network costs.

If it was possible to take advantage of the mainstream technologies also in the PSS

sector, networks could be built much more cost efficiently. The basic assumption is that

elements from mass production could be utilised and only minor modifications would be

needed to fulfil the PSS requirements. However, if major modification to mainstream

elements were required, the approach might be more costly than the use of dedicated

technologies.

2.1 Research problem and objectives

The target of this thesis is to evaluate whether it would be sensible to implement PSS

networks based on mainstream technology. The comparison will be done between the

standardised technologies TETRA and GSM. Dedicated networks have the advantage

that the products have been developed especially for their specific end-user groups

which have different requirements than end users in public mobile networks.

Additionally, dedicated networks are regarded as more suitable for mission critical

tasks as interference from other network users can be minimized.

On the other side, the use of mainstream technologies could give the possibility to

utilize achievements in the mainstream market also for PSS users. The fast

development in public mobile telephony has reduced the prices of certain network

elements significantly and also led to an extremely fast technical development.

of 64

Technical as well as economic arguments need to be evaluated. An analytic

hierarchical process (AHP) will be used to combine the results of the different

dimensions and to simplify the decision process.

2.2 Background

In most European countries, PSS users use over-aged analogue radio communication

systems. These systems typically have local coverage and communication between

different districts as well as between different user organisations may be very difficult.

The independent radio systems do not support cross border group communication.

This is regarded as a major handicap, for example, for highway patrols which need to

reregister themselves every time when moving over a district border. This process is

time-consuming and the delay may be critical in emergency situations when police

forces need to rely on proper communication means. Other restrictions to the operation

are, for example:

• No authentication of the radio terminals

• No air interface encryption

• Calls between different agencies are hardly possible

• Calls are limited to a small geographical area

• Low data transmission rates

The critical situation has been realized and in most countries basic decisions have

been made that the PSS networks should be replaced by new, digital technology.

However, many governments have not yet decided what kind of technical solution to

utilize to implement a future network. This might be astonishing, since as early as in

June 1995 Schengen Telecom published the functional specifications for PSS users.

ETSI confirmed in 1996 that TETRA, which is the only standard for PSS accepted by

ETSI, fulfils the requirements [23]. The main reason to accept only one standard is to

guarantee cross border communication over whole Europe.

The economic downturn at the beginning of the 21st century has brought new

arguments to the discussion. Most governments have been forced to cut their

expenses dramatically. At the same time, many telecommunication operators and

manufacturers have been seeking new markets. As the commercial mobile telephony

market seems to be stagnating, there seems to be a huge potential in the PSS

segment. As a result, a variety of technological solutions for PSS networks have been

of 64

offered lately. The main competition is assumed to be between TETRA, Tetrapol and

GSM.

This thesis takes as an example the current PSS case in Germany because it will be

among the largest PSS networks in Europe with borders to many other European

countries. Therefore, the technology selection in Germany will have a strong influence

on the decision in other European countries.

Decision-making seems to be difficult due to the lack of references. For the time being,

only one countrywide, multi-agency network is in full operation: the VIRVE network in

Finland which uses TETRA technology from Nokia. A few other TETRA networks are

under construction and some single-agency networks using Tetrapol technology are in

operation as well.

2.3 End-user- requirements

In addition to the economic arguments, the fulfilment of the end-user requirements is

important for the selection process for a suitable technology. Because of the mission-

critical tasks of the end-users, the whole system must be highly available. Redundancy

and resilience play a key role. This is not only a question of the selected technology but

is also strongly related to network planning and dimensioning. The most common PSS

requirements will be discussed below.

2.3.1 Network functions

Under network functions we understand functionalities, how they are seen by the end-

user. Hence, we are here not focussing on the technical implementation, but on the

available services for the users.

• Group calls: Semi duplex point-to-multipoint communication which means that

only one member of the group is allowed to speak at a certain point of time. In

PSS networks typically about 80% of the speech traffic in a network is

generated by group calls.

• Closed user groups: Every user in the system belongs to an organisation (e.g.

police Helsinki). Depending on his or her call rights, a police officer is able to

communicate only within the own organisation or, in addition, to certain other

organisation’s groups. Closed user groups allow the implementation of true

multi-agency networks. Sharing the network between organisations does not

only allow easy cross-organisational communication, but it also uses the

resources more efficiently.

of 64

• High priority calls: The infrastructure gives the possibility to assign different

priorities to different users, organisations or call types, which results in better

grade of service. Priorities may be given in resource queuing or speech item

allocations.

• Pre-emptive speech services: In certain cases, like emergency calls, it must be

ensured that resources can be allocated immediately to a call. If all resources

are busy, another call must be dropped or queued. Pre-emptive speech item

means, that a group member with higher priority may interrupt another user’s

speech.

• Base station fallback: If the base station loses contact with the exchange or the

exchange is out of operation, the base station may enter a so-called fallback

mode, where calls within the base station area are possible.

• Direct mode: If a mobile is out of coverage it may communicate directly with

another mobile without using the network infrastructure. This operation mode

may be necessary in tunnels, basements or in case of complete failure of a

base station.

2.3.2 Network security

The network should be secure from eavesdropping or spoofing but the security barriers

should not compromise the network functionality. The main features related to security

are:

• Authentication: The network will authenticate mobile terminals upon registration

in order to avoid unwanted users. In a similar way, the terminals may

authenticate base stations to ensure that they never register to a fake base

station.

• Air interface encryption (AIE): Protects against tracing and eavesdropping on

the air-interface. All signalling information, including user ID as well as speech,

is encrypted. Encryption and decryption are done in the terminals and in the

base stations.

• End-to-end encryption (e2ee): For certain organisations it may be necessary for

the speech to be encrypted throughout the whole network infrastructure.

Encryption and decryption are done at the end-points of the communication

path. It is important to understand that e2ee does not encrypt any signalling like

of 64

roaming or call set-up; therefore, AIE and e2ee are complementary and not

alternative solutions.

• Dynamic keys: Encrypting and decrypting data requires keys. These keys may

be static or dynamic. Static keys need to be changed manually and often

require reprogramming of the terminals. Dynamic keys are changed frequently

e.g. during the roaming process. Encryption with dynamic keys is the more

secure solution, since old keys are not reused and unauthorized decryption of a

message is therefore more difficult.

Security requirement may vary between user groups. Fire brigades typically do not

require encrypted speech, but for the police, for example, it is essential.

2.4 Group call related feature descriptions

Some of the main features used in group-calls are described here in more detail since

they are important for the overall understanding of the discussion below. We will see

later that the push-to-talk functionality and the group call area type have high impact on

the network capacity which again has major economic impact. The other features are

mainly perceived as network functions by the end-user.

2.4.1 Push-to-talk functionality

In contrast to public telephony, the group communication in PSS networks does not

use number dialling through a keyboard. Instead, the users typically have an active

group selected all the time. They are automatically listening to the communication and

if they wish to speak, they just need to press the PTT (push-to-talk) button. There are

different ways to allocate resources for such a call.

Message trunking means a permanent reservation of a traffic channel for the complete

duration of a call. If the radio channel is on air permanently, one speaks also about an

open channel. Since it is economically not sensible to keep the communication channel

open also during silent periods, modern PMR networks use so-called transmission

trunking which reserves channels only during the time when a speech is ongoing.

Drawback of this solution is, that high amount of call set-up signalling is required, since

every single speech item of a group member needs new channel allocations.

Based on the fact that speech items of group calls typically appear in bursts, so called

quasi-transmission trunking is a commonly used alternative. It is a trunking method

where a traffic channel is allocated for a certain call transaction (while the push-to-talk

button is activated) and the channel de-allocation is delayed for a short period at the

of 64

end of the transaction (after releasing the push-to-talk button). This means that if a new

speech item arrives during that hold time, no new channel allocations are required.

There is no off-hook signalling in a push-to-talk call, which means that speech is

directly connected and therefore fast call set-up times are an important requirement.

Typically values less than 0.5 seconds should be achieved.

2.4.2 Group call area

Groups are typically communicating in areas which can be defined by the network

management. If a base station belongs to a group call area, it means that a

communication channel will be allocated to that site if there is communication in this

group ongoing. If we are speaking about a so-called fixed group area, the resources

are allocated independently whether there are group members registered at that site or

not. In case of large group areas consisting of many sites or groups with only a few

members, this leads to a very inefficient usage of resources.

Another approach is the so-called shifting group call area, where the system first

checks where the members of the group are registered and then allocates the channels

only to those sites. This feature allows large group areas without wasting resources.

However, it is important to understand that in case of shifting group calls handovers to

other sites must still be supported. For example, if during a call a member moves to a

site where there has not been any group member at the beginning of the call, the

system must allocate resources to this new cell. This is regarded as especially

important in regions with small cells, like urban areas, since the probability for

handovers is high. The support of handover is also a must if message trunking is used,

since the long call durations increase the probability for cell changes during the call.

2.4.3 Dynamic group number allocation (DGNA)

It is possible to build groups which are only temporary. For example, if some policemen

and some ambulance officers need to communicate during a certain incident, the

dispatcher can assign to them a new, temporary group number. This allows quick and

easy communication between different organisations.

2.4.4 Priorities

In an organisation, different users or call types may have different importance.

Basically there are resource and speech item priorities. Both can be pre-emptive or be

used for queuing only.

of 64

A resource priority means that if all resources at a base station are occupied and

different calls need to queue, the call with the highest priority will be served first.

Speech item priority means that if two persons would like to speech at the same time,

the user with the higher priority gets the speech item.

2.4.5 Late entry

It may happen that a mobile is engaged in an individual call when the group call is set

up or a mobile moves into the group area while the call is ongoing. In this case the

system may send late entry signalling on the control channel to ensure that these

mobiles can join the group call.

2.4.6 Scanning and priority scanning

A radio subscriber can be a member of different groups at the same time. However,

only one group at the time is active; that is the group he or she is talking to when

pressing the PTT. The other groups can easily be selected using the group selector on

the mobile terminal.

Priority scanning allows giving different priorities to the scanned groups, which means

that if the user has selected a group of lower priority and some communication is

ongoing on a group with higher priority he may be forced to change group.

2.4.7 Data calls (SDS and status)

Short data services (SDS) give the possibility to send text messages simultaneously to

all members of a group. The sending unit may be a mobile or a dispatcher station.

Status messages are a special form of SDS indicating e.g. the working status of the

sender. In this case the message contains only a short number which is trans-coded in

the terminal to an informative text like “on duty”, “off duty” or “call back request”.

2.5 Available technical solutions

For the upcoming cases in Europe, the main competition is supposed to be between

the following three different technical solutions: TETRA, GSM and Tetrapol. The focus

of this study is to evaluate the attractiveness of mainstream technologies for the PSS

target market. As a proprietary solution, Tetrapol is not in the scope of the study and

will only be introduced shortly since it has a significant market share.

of 64

2.5.1 TETRA

TETRA (TErrestrial Trunked Radio) is an open digital trunked radio standard [4]

defined by the ETSI (European Telecommunications Standardisation Institute) to meet

the needs of the most demanding professional mobile radio users.

TETRA uses TDMA technology with 4 timeslots at a bandwidth of 25 kHz per carrier.

The standard defines the air interface, the peripheral interface and the inter-system

interface. The architecture within the system infrastructure is not standardized. There

are various manufacturers for infrastructure, mobiles and applications. Main players in

the infrastructure business are Motorola, Nokia and Rhode & Schwarz.

The proper interoperability between mobiles and infrastructure of different

manufacturers is guaranteed by so called TIP specifications (TETRA Interoperability

Profiles). TIPs are published by the TETRA MoU which represents user organisations

and manufacturers.

2.5.2 GSM ASCI

GSM (Global System for Mobile communications) is an open standard for digital

cellular telecommunication systems. Its target market is point-to-point communication

for private or business users.

GSM uses TDMA technology with 8 timeslots at a bandwidth of 200 kHz per carrier.

Besides the air interface, the GSM standard also defines the interfaces between the

networks elements allowing full multi-vendor environment within the infrastructure.

The specifications have been extended with some basic group call functionalities, the

Voice Group Call Services (VGCS) [10] and Voice Broadcast Service (VBS) [11]. They

are part of the GSM ASCI (Advanced Speech Call Item) [5] which is used, for example,

in GSM-R. Main target markets are railways, where the group call is set-up in a clearly

defined area, along the track.

The main advantage of GSM ASCI is that it can share the resources of an existing

GSM network. The high penetration of GSM networks worldwide makes such a solution

look very attractive for many countries. However, even though GSM ASCI has been

awarded to a high number of railway customers, there are currently no PSS networks

existing based on GSM technology.

of 64

2.5.3 Tetrapol

Tetrapol has been developed for PSS markets based on the requirement of the French

police forces. Currently the technology is in operation or implementation phase in 15

PSS networks worldwide [26].

Tetrapol uses FDMA technology providing one speech or control channel per 12.5 kHz

carrier. In practice this means that Tetrapol solutions are mainly competitive in

networks with few users covering a large area, which is typically the case in single

agency networks.

Even though the name of the product reminds of TETRA, Tetrapol has nothing to do

with the ETSI TETRA standard. Tetrapol is a proprietary solution from EADS Telecom

(former Matra) and has never been accepted as an ETSI standard. The Public

Available Specifications (PAS) [25] can be ordered from the Tetrapol homepage. They

give the possibility for other manufacturers to develop infrastructure, mobiles or

peripheral applications which are fully compliant with Tetrapol.

The PAS give theoretically the possibility for multi-vendor environment; however,

practice has shown that EADS is still the only infrastructure and terminal manufacturer.

Tetrapol partners consist mainly of application partners and resellers.

of 64

3. EXISTING ANALYSIS

The possibility of using a GSM solution for the next generation PSS networks with

national coverage has been analysed deeply in Scandinavia and Germany during 2002

and 2003. Two major studies have been made on behalf of the Norwegian government.

The first one is a report from Nexia and Preview about convergence of wireless

networks [18] and the second one is the evaluation of the previous report from Gartner

[15]. At about the same time, Nick Smye published a report on the use of commercial

cellular networks for PSS in Norway [22]. Nokia has published a related white paper in

2002 [19].

Berit Rollén wrote a report on behalf of the Swedish Government [21] covering end-

user requirements and different technical solutions. He also compares experiences

from different countries and how the projects are proceeding.

Professor Walke’s expert report [31] on the usefulness of the Vodafone network for

public safely and security compares existing TETRA functionalities with possibilities of

GSM including optional proprietary solutions. The report has been made for Vodafone

Germany. Gartner draws related future perspectives in the report “Europe’s Standard

Shows Way Forward for Private Mobile Radio” [14].

The Danish government made detailed investigations [2] and compared TETRA with

GSM and possible UMTS based solutions. The report, which highlights the user

requirements, is based on the analyses from Accendure [1]. Besides the technical

comparison, Accendure is also focussing on the overall cost impact for a network

operation over 15 years.

Even though the reports have basically same inputs, they come to very different

conclusions. The chapters below contain a short review of the main arguments.

3.1 Network functions

In this section the network functionalities that are perceived by the end-users are

described. Note that fast call set-up times are also seen by the end-user, but their

impact is strongly related to network capacity. That is why this issue is discussed in the

next section.

3.1.1 Group call memberships

The dynamic creation of groups is not standardised in GSM. Nexus suggests as a

solution the usage of conference bridges which would combine different smaller groups

of 64

to one large group and allow cross-organisational communication. According to Walke,

a proprietary solution, in which dynamic group allocations could be done in a similar

way as it is standardized for TETRA, will be more likely. Group numbers could be

transmitted over the air interface and be programmed to the SIM card of the mobile.

According to Gartner, none of the proposed GSM solutions is suitable. They mainly

assume that the market is not large enough to gain support from manufacturers for this

kind of special enhancement.

3.1.2 Handover times

Only Walke covers the handover issues in detail and refers to the fact that GSM is

supporting seamless handover for the talking party in a group call which is the same

functionality as known from normal duplex calls.

However, listening subscribers in a group call do not support seamless handovers. This

restriction is valid for GSM as well as for TETRA. GSM uses the so-called idle mode

cell reselection which means that a subscriber returns to the control channel of the new

cell. From there it will be invited to the group call by late entry signalling. Tests on a

GSM-R network have shown communication breaks of 1.4 to 16.8 seconds with a

random distribution [17]. This procedure could be optimised, but an additional receiver

in the mobile would be required to receive group call signalling during the call [22].

TETRA specifies undeclared handover signalling [4] for listening subscribers in the

group call; typical speech breaks are in the range of 1 second, however, independent

measurement reports do not exist.

3.1.3 Priorities

Queuing priorities are supported by both systems. Generally no major concerns are

stated except the capacity considerations mentioned below. Also pre-emptive priorities

are available for both systems.

Regarding speech item priority, Smye mentions that they are not supported in GSM

group calls. A speech item is always allocated based on first come first serve basis

without queuing. Only dispatchers have the right to reserve the downlink for

themselves. In TETRA, speech items are allocated based on a priority queue, where it

is possible to allocate higher priority to certain members.

of 64

3.1.4 Data messages (SDS and status)

TETRA supports sending of text-messages simultaneously to all group members. The

GSM ASCI group call features are related to speech calls only, thus data messages to

groups are not supported. Walke mentions also Cell Broadcast Service which allows

sending of messages to all users within one cell. This can, however, not be regarded

as an alternative solution since generally different user groups are located in one cell.

3.2 Network capacity

The existence or non-existence of some features has major impact on the required

system capacity. It is important to focus also on possible combinations of features in

the way they will be used in real networks.

3.2.1 Coverage & Capacity

Walke states that a newly built TETRA network can hardly achieve similar high

coverage as an existing GSM network. GSM provides nearly complete coverage in

highly populated areas not only outdoors but also indoors, where TETRA is planned to

have a statistical coverage location probability of 95% only.

Objective of a PSS network is to guarantee coverage and incident capacities also in

low populated areas, like border or costal areas, since accidents often occur in these

kind of regions. For economic reasons it is according to Gartner not possible to provide

satisfactory coverage with GSM in countryside regions. This comes from the fact that

GSM cell sizes are significantly smaller than TETRA cells. The network capacity and

coverage in GSM networks is driven by commercial arguments where for TETRA the

main driver is the functional requirement of the PSS users.

In order to fulfil incident capacities, the network should support different call priorities.

Call priorities are specified in the GSM standard (ASCI) but for the time being they are

hardly implemented in existing networks. In TETRA, however, traffic prioritisation is a

standard feature. There is no practical experience in how a network will react if normal

and high priority traffic will reach their peak simultaneously, as this may be the case in

major accidents and catastrophes.

3.2.2 Call set-up times

The requirement for group call set-up times is typically 0.5s [32]. Measurements have

shown [17] that GSM based solutions require between 1 and 3s for group call set-ups

and up to 4.5s if a mobile dispatcher is included in the call.

of 64

Because it is not possible to achieve the requirement with GSM, Nexus and also Walke

suggest the following solution. After an initial call set-up, the traffic channel would be

kept open for a longer period of time. In this case, the initial call set-up takes 1 to 4.5

seconds and afterwards, during the conversation, the allocation of speech item can be

done within the specified period. Walke even suggests that frequently used group

channels could be left open all the time, which would be the only solution in order to

completely fulfil the user requirement.

In practice this means that message trunking or even open channels would be used

instead of transmission trunking. Gartner mentions that such an implementation would

have enormous impact on network load and is therefore unrealistic. They also state

that it may be technically possible to reduce the initial call set-up time to below one

second for GSM. However, this would require significant enhancement in the network

infrastructure and cause enormous upgrade costs.

3.2.3 Group call area

The support of shifting area group calls is hardly covered in the reports, even though it

may have major impact on the capacity requirement of the networks.

GSM gives the possibility to activate traffic channels for group calls only on sites where

subscribers are listening to the call [31]. However, since handovers are not supported,

subscribers, which are moving within the group area to a cell that has not been active,

will be excluded from the call. Walke suggests that in addition to all sites where

members are located, also all adjacent sites would be activated. This way, the first cell

change during a call would succeed, but the second one might fail again. Therefore,

shifting area cannot give reliable group call coverage and can hardly be utilised as a

bypass in GSM networks. This might be also the reason why it has not been discussed

in detail in the other reports.

3.3 Network security

The encryption algorithm TEA2, which is in use for TETRA, has been especially

developed to meet the Schengen requirements. Smye mentions that any PSS solution

in Norway will have to comply with these requirements. Therefore, the security level of

the GSM air interface encryption is not regarded to be high enough. According to

Nexia, however, security requirements can be met by add-ons on top of the GSM

solution without mentioning any details on how such a solution might look like.

of 64

Walke mentions that in a GSM group call, only the talking party is authenticated, the

listening party is not [8] [10]. A mobile is able to join a group call as soon as it has a

valid group ID programmed to its SIM card. He supports the opinion that group calls

are still safe since counterfeiting of SIM cards has not been encountered for the time

being.

Over the air key distribution is not specified in the GSM standard. This implies that

static keys need to be used for the encryption. For PSS, dynamic keys should be used

in order to guarantee a high level of security against eavesdropping. In order to

implement dynamic keys, Walke suggests a proprietary solution for over the air key

distribution in GSM networks.

Regarding end-to-end encryption (e2ee), the two platforms GSM and TETRA are quite

similar, since they are both supposed to be transparent and therefore able to support

different kind of e2ee solutions. Gartner states that GSM e2ee mobile are most

probably more expensive than TETRA mobiles because the low volumes are not

attractive for many mobile phone manufacturers.

3.4 Economic arguments

Cost efficiency is one of the key arguments for GSM ASCI. Basically it is assumed that

the entire infrastructure from an existing GSM network could be used for a PSS

network and only minor software upgrades would be required. In case of TETRA, only

transmission equipment and base station sites could be reused and the rest needs to

be built up from zero. The real cost impact of these differences seems to be very

difficult to estimate, and only little evidence is given in the reviewed reports.

3.4.1 Network infrastructure

According to Accenture, the investment costs for a TETRA network would be about

31% higher than for a GSM ASCI network. This comparison is related to standard ASCI

features only and it is stated clearly that the functionality of the GSM network would be

much lower compared to the TETRA solution. The cost effect for enhancing the GSM

ASCI functionality by proprietary solutions as described by Walke has not been taken

into account in any of the reports.

Operating costs are estimated to be roughly the same for the two solutions. The overall

net present value including all capital and operating costs for a TETRA network is

according to Accenture supposed to be about 5% higher than for a GSM based

solution.

of 64

3.4.2 Radio terminals

During the last decade, GSM mobiles have become significantly cheaper. Using

standard GSM products for PSS would automatically mean that also PSS terminals

based on GSM technology would be less expensive than TETRA terminals. This

statement from Walke stands very much in contrast with Gartner’s opinion.

GSM terminals lack most of the key PSS functionalities, which means that the PSS

market cannot take advantage of the mass products from GSM. As example they

mention that currently available GSM terminals supporting e2ee cost 30000 NOK (3500

€), which is about 3 times the price of a standard TETRA terminal. Additionally the

functionalities like DGNA and direct mode would need to be added to a standard GSM

mobile. Their implementation costs have not been taken into account in any of the

reports. Accenture’s analysis assumes similar prices for GSM ASCI and TETRA

Terminals.

Because of the lack of group call signalling to the listening members of a group call,

e.g. for receiving SMS or scanning information, a second receiver would be required in

GSM ASCI terminals, if these features should be implemented. This means according

to Smye that no standard GSM terminals could be used. This would not only increase

the size and power consumption of the terminals, but also the price, as it is not a mass

product anymore. Additionally Walke suggests using the TETRA modulation and

frequency band for direct mode in GSM ASCI terminals, which would require dual

mode operation between GSM and TETRA.

Among the major five GSM terminal manufacturers (Nokia, Motorola, Sony-Ericsson,

Siemens and Samsung), only Siemens produces GSM-R mobiles. Ericsson offers

GSM Pro and proprietary EDACS mobile radio terminals. On the other side, TETRA

terminals are available from Nokia, Motorola and Sepura and several other

manufacturers. It seems that there is a very low manufacturer interest in developing

special GSM terminals for relatively low market volumes.

3.4.3 Risk factors

Regarding the rollout, a GSM based solution would offer decent coverage right from

the start. In a TETRA network, the coverage needs to be built up from the beginning.

This risk for a delay in the rollout is mainly related to the availability of base station

sites und is thus not directly related to the technology. The VIRVE network in Finland,

for example, could be rolled out on schedule [13].

of 64

Especially Walke suggests numerous proprietary solutions, so called Vodafone add-

ons in order to fulfil the technical requirements. The availability of these kinds of

solutions within the set time frame is questionable, since the development of new

features and their rollout always implies a certain risk. Gartner sees a high

technological risk in using mainstream technologies for the time being, as the solutions

are not mature. Most of the reports mention that GSM based solutions are not

implemented in any country for PSS users.

The interest of commercial operators in entering the PSS business is according to

Accendure very low. The amount of users is small compared to the public users and

there are limited growth expectations. Existing users may perceive degradation of

service which leads to loss of revenue and may even have impact to customer loyalty.

Since a large amount of software and hardware upgrades would be required, there is a

high implementation risk associated in live commercial networks.

3.5 Summary of literature review

On technical level, the group call functionalities offered by TETRA and GSM are only

comparable if additional unspecified features will be added to GSM ASCI as detailed

described by Walke. It is, however, unlikely that future PSS networks will be based on

proprietary solutions.

Such an approach would bear high technology risks. It took many years for TETRA to

become a mature technical solution and it is very unlikely that a GSM based solution

would be available within the next years. The gaps are far too large, like for example:

• Terminals for PSS use do not exist – the development of mature terminals will

take years.

• Missing authentication of group members in a call is unacceptable for mission

critical use.

• GSM air interface encryption algorithm is not safe enough for PSS usage.

• Slow call set-up times are outside the acceptable range – improvements would

take years to develop and implement.

• Missing shifting area group call has enormous impact on capacity.

Even on economic level, it is uncertain whether a GSM approach can be cheaper. The

implementation of the ASCI features requires changes in nearly all network elements.

of 64

Additionally, coverage needs to be extended to border areas, which can be very costly

because of the small cell sizes in GSM. GSM ASCI Terminals would be most likely

more expensive than TETRA terminals, especially if direct mode and other PSS-related

features need to be implemented.

Missing references will make it difficult to prove the maturity of a GSM ASCI solution. It

is rather unlikely that PSS customers will accept a technical approach that has not

been tested elsewhere.

of 64

4. HIERARCHICAL ANALYSIS

In the following chapter, the differences between TETRA and a GSM solution will be

analysed in three dimensions. The first dimension compares the ETSI specifications

and points out which functions are available according to the standard. Proprietary

solutions will not be discussed on that level. The second dimension, a technical

analysis, discusses how the end users and the operators perceive the differences

between the network-solutions. Proprietary approaches will only be taken into account,

if they form a feasible alternative to fulfil a given requirement. Finally, a third dimension,

an economic analysis, focuses on the cost of the two alternative solutions, including

capital and operational costs for the network infrastructure and end-user terminals. The

availability of the solution and its related technology risk will also be discussed in this

chapter.

The methodical approach will be an analytic hierarchy process [27]. Since there is a

very strong correlation between the first and the second dimension, the results from the

comparison of the air interface specifications will be used as an input for the technical

analysis. Therefore, only the results from the technical and economic analysis will be

used to derive final conclusions. The picture below shows the structure of the

hierarchical analysis. The weighting of the different levels will be discussed in the

summary of each subchapter and in section 4.4 Combination of the results:

Analysis

OPEX Risks Network Security

CAPEX Network Capacity

Network Functions

Economic Technical Analysis

Overall Result

Figure 1: Structure of analysis

Three different network solutions will be discussed:

• A new, independent TETRA network

• A GSM ASCI network which is based an existing GSM network

• A GSM ASCI overlay network which is based on an existing GSM network

where only part of the cells are upgraded to support group call functionalities.

This approach assumes a certain cell overlapping in the GSM network.

of 64

4.1 Air interface specifications

Group call functionality has an effect on nearly all elements in the network. For TETRA

only the air interface is specified; the core network, including, for example, the

signalling between base station and exchange, is manufacturer specific. In contrast,

the GSM standard specifies also the interfaces between the network elements. The

analysis focuses on the air interface specifications since they can be compared directly

between the two standards. Impacts on the core network will be mentioned as far as

they are relevant.

4.1.1 GSM ASCI

The ASCI (Advanced Speech Call Item) have been originally developed by ETSI and

UIC (International Union of Railways). Therefore, the functional specifications are

targeted firstly on railway communications. The ASCI features are part of GSM phase

2+ and consist of the following three items [5]:

• Voice Group Call Service (VGCS) – A teleservice

• Voice Broadcast Service (VBS) – A teleservice

• Enhanced multi-level precedence and pre-emption service (eMLPP) – A

supplementary service

None of the ASCI features can be used with phase 1 or 2 mobiles. This means that

dedicated terminals are required. Fallback and direct mode are both not defined in any

GSM standard. An implementation would require proprietary solutions.

4.1.1.1 Enhanced Multi-Level Precedence and Pre-emption service (eMLPP)

The service consists of two parts – precedence and pre-emption [7]. Precedence

allows assigning priority levels to calls in combination with fast call set-up. If a higher

priority call is set-up when all resources are in use, pre-emption allows seizing of lower

priority resources.

There are 7 different priority levels. The two highest ones are reserved for network

internal use (e.g. for specific broadcast calls) and are only available for calls within one

MSC area. Additionally three different classes of set-up time performance levels are

defined. For each user in the network, the maximum precedence level may be defined.

If the user does not use eMLPP services, the network uses a default priority. Calls of

highest priority and fast call set-up do not require authentication nor encryption on the

radio link. Authentication and encryption may be postponed or omitted.

of 64

The information about the different precedence levels is stored in the SIM of the

mobiles and in the HLR/VLR of the network. Implementation of the feature requires

new features and parameters in MS, BTS, BSC and MSC. User data storage is needed

in SIM and HLR/VLR.

4.1.1.2 Voice Group Call Service (VGCS)

VGCS gives the possibility to establish group calls in a GSM cellular network [8] [10]. A

group call has basically three different participants: The talking subscriber, the listening

subscribers and the dispatchers. Talking and listening subscribers can only participate

in the group call, if they are within a predefined group area and if the group ID is stored

to their SIM. Dispatchers can be located anywhere in the network and they are

identified by MSISDN or ISDN. The maximum amount of dispatchers in a call is five.

This restriction is caused by the definition of the conference call.

The service requires a new network element, the Group Call Register (GCR). It

contains group details such as group area and dispatchers. The interface between

MSC and GCR is not specified and therefore vendor specific. The group IDs are stored

in the mobiles’ SIM; updating of subscriber data over the air interface is not considered

in the current specifications. This means that DGNA is not supported.

For the calling subscriber, a standard call set-up procedure, depending on the priority,

is done. The BSC allocates resources and then invites the group members to the call

using the new logical channel Notification Channel (NCH). The NCH sends the

information for the whole duration of the call. This allows group members which are in

the beginning of the call outside the group area, to join the call (late entry).

The network may pre-empt resources of lower priority. This is possible for emergency

calls based on the specifications for eMLPP which are described above.

Only one mobile subscriber can talk at any moment, the other participants can listen to

the common downlink channel, which means that if several subscribers are located in

the same cell, they will listen to the same channel. By pressing the PTT, a listening

subscriber can request a speech item. Speech-items are allocated on first come first

serve basis without queuing. The talking subscriber always reserves a separate traffic

channel on the uplink. The dispatchers can talk at all times and their speech is

connected to the common downlink channel.

For the talking subscriber, standard handover procedures can be used within the group

area. Listening subscribers have to initiate the handover themselves, since the system

of 64

does not have any information about the users in the call. Seamless handover is not

supported; idle mode cell reselection has to be used. A dispatcher uses standard

handover procedures.

The described group functions are related to speech only. SMS to group numbers are

not supported. A listening subscriber cannot receive any signalling while in the call,

which means that e.g. sending and receiving of SMS during a call is not possible.

The calling subscriber or a dispatcher can terminate the call. Termination through

inactivity after expiring of a timer is also possible.

For the calling subscriber, authentication and encryption are optional. They may be

omitted or postponed when using fast call set-up. For listening subscribers,

authentication is not possible and encryption is optional.

Like for eMLPP, modifications in all major network elements are required in order to

support this feature. These are MS, BTS, BSC, MSC, VLR/HLR and SIM. Additionally

the implementation of GCR is needed.

4.1.1.3 Voice Broadcast Service (VBS)

VBS consists of the same functionalities as VGCS with the difference that the speech

is unidirectional [9] [11]. The calling subscriber may be a mobile user or a dispatcher.

No uplink functionality is required for the listening subscribers. The network

requirements are similar as for VGCS.

4.1.2 TETRA

The group call functionalities are defined in the ETSI specifications Terrestrial Trunked

Radio (TETRA), Voice plus Data (V+D), Part 2: Air Interface (AI) [4]. These

specifications also include the signalling for fallback and direct mode, however, they

will not be discussed since a comparison to GSM is not possible.

Every TETRA subscriber, mobile or dispatcher, is identified by an ITSI (Individual

TETRA Subscriber Identity). A group is identified by a GTSI (Group TETRA Subscriber

Identity). The ITSI/GTSI consists of a country code, a network code and the subscriber

identity. A mobile may be member of different groups at the same time and it sends its

membership-information to the Switching Infrastructure (SwMI) upon registration. The

group information, like group area and members, is stored in the SwMI. The standard

specifies updating of group information to the mobiles over the air interface (DGNA), for

example, by authorized dispatchers.

of 64

When initiating a call, the subscriber sends the GTSI on the MCCH (Main Control

Channel) to the SwMI. The SwMI allocates one traffic channel on every site within the

group area and invites the mobiles to the call. Optionally it may reserve resources only

on those sites, where members are located (shifting group call area). Priority queues

are used to allocate resources. Pre-emptive services are also supported.

Group calls are always established as semi-duplex calls for all subscribers. By pressing

the PTT, a listening subscriber can request a speech item. Speech-items are allocated

using a priority queue. The talking subscriber uses the already allocated TCH (traffic

channel) on the uplink.

In contrast to GSM, the mobile always initiates handovers in TETRA. The standard

describes three different types of declared handovers. Seamless handover is

supported for the talking subscriber. The listening subscriber can make an undeclared

handover, which means that the mobile needs to move to the control channel of the

new site from where it will be commanded to a traffic channel. If a subscriber moves to

a cell within the group area where no TCH is active for the call, the SwMI has to

allocate a TCH to the group call for that subscriber.

Since quasi transmission trunking is commonly implemented, the call will be terminated

after expiring of a certain hang time. The standard also allows termination through the

calling subscriber or a dispatcher.

Authentication is done during registration and roaming. The standard supports

encryption with static or dynamic keys.

4.1.3 Comparison of specified features

Since TETRA has been especially developed for group calls, it fulfils most of the

requirements. Some of the limitations in the table below are stated as “unlimited”. They

reflect the standard; effective limitations are, however, manufacturer specific.

Shifting group call area is basically possible for both technologies, TETRA and GSM

ASCI. The air-interface specifications do not mention the implementation, since

resource allocations are part of the core network functionalities. Several manufacturers

have implemented the feature for TETRA; however, for GSM it does not exist. An

implementation would require major modifications in the core network software, which

is for economic reasons not feasible.

of 64

TETRA GSM

ASCI Resource queuing priorities Yes Yes Resource pre-emption Yes Yes Speech item priorities Yes No Speech item pre-emption Yes No Late entry Yes Yes Maximum group size Unlimited 1024 Maximum amount of dispatchers in group Unlimited 5 Maximum amount of sites in group call Unlimited Unlimited Amount of groups per subscriber Unlimited 50 Fixed group area Yes Yes Shifting group area Yes No Used traffic channels for a group call on N sites with X mobile dispatchers

N N+X+1

Authentication of talking subscriber Yes Optional Authentication of listening subscriber Yes No Seamless handover for talking subscriber Yes Yes Fast handover for listening subscriber ~1s No Table 1: Summary of technical comparison

All above-mentioned features are input-information for the functional and operational

comparison in the next chapter. Therefore, table 1 has not been taken into account in

the hierarchical analysis process.

4.2 Technical analysis

The section below analyses, how the end-users and the network operators perceive

the functionalities described in the previous section. It also discusses, which are the

restrictions caused by certain solutions and how strong impact they have in practical

situations. The section is divided into three parts: network functions, capacity and

security.

4.2.1 Network functions

The network functions reflect which services are available for the end users including

dispatchers and mobile users. Services, which have direct impact to capacity, will be

discussed in a separate chapter. In contrast to commercial networks the functions also

include network management tasks like the creating of groups. This so called tactical

management allows dispatchers, for example, to create new groups for an upcoming

mission (DGNA).

of 64

4.2.1.1 Group size

The TETRA specifications do not mention any group size restriction. Limitations are

vendor specific. In case of Nokia SwMI, the amount of radio subscribers in a group is

not limited and the amount of dispatchers in a group call is 30.

GSM ASCI limits the amount of mobile subscribers in a group to 1024 and the amount

of dispatchers to 5. The first limitation may be significant for broadcast group calls to

large organisations. The second limitation is especially critical if different organisations

are involved in a group call. Cross-organisational communication is important, for

example, during a major incident; see also below (DGNA).

4.2.1.2 Dynamic Group Number Allocation (DGNA)

A dispatcher has to be able to allocate mobiles to temporary groups. This allows

allocating resources for a mission, even if the mobile users belong to different

organisations.

For GSM ASCI, there are different solutions to bypass the non-existence of DGNA:

• A set of pre-programmed groups could be used for special missions. However,

this approach is hardly applicable for cross-organisational communication, since

it highly compromises the numbering flexibility.

• A conference bridge could be used to combine groups of existing organisations

[18]. This would reduce the amount of included dispatchers because of the

limitation of 5 participants in a conference call.

• Proprietary solutions for over the air programming of the group data via SMS

have been considered [31]. This seems to be the only acceptable solution for

end-users.

The operators and end-user organisations should be aware of the fact that proprietary

solutions often have negative influence on interoperability. Furthermore, the lack of

competition typically causes higher equipment prices.

4.2.1.3 Short data messaging

The sending of short data messages to groups is a very effective way of informing the

members of a group during an incident. This feature is supported by TETRA but not by

GSM ASCI.

of 64

The sending of individual messages, as bypass, is significantly slower and causes

additional load on the signalling channel. This increases the risk for control channel

congestion during peak loads like emergency situations. Additionally, it is not possible

to send individual SDS to mobiles which are engaged in a group call. This solution is

not acceptable for the use in critical situations.

4.2.1.4 Call priorities

Queuing and pre-emptive priorities are specified for TETRA as well as for GSM ASCI.

Difference is that in GSM priorities are associated to subscribers. In TETRA different

priorities can be given to subscribers or groups which lead to higher flexibility.

Furthermore, TETRA supports more priority classes than GSM ASCI.

Main difference, however, is the lack of speech item priorities in GSM. In emergency

situations it is important that a group leader can get a speech item and force the others

to listen in order to achieve organised communication.

4.2.1.5 Priority scanning

No signalling for priority scanning is specified for GSM ASCI. If a member is engaged

in a group call, she or he is not able to receive any signalling. This restriction may be

very critical for PSS users, where certain high priority group communications need to

be available even if some of the members are engaged in another group call.

4.2.1.6 DMO and base station fallback

In case the mobiles are out of network coverage or the connection between exchange

and base station is down, for example, due to a major accident, GSM based mobiles

are not able to communicate. No base stations or mobiles supporting these

functionalities are available on the market for the time being. The TETRA standard

specifies both functionalities.

4.2.2 Network capacity

The required network capacity depends on different factors, like cell size, support of

shifting area group call and the end-user requirement for call set-up times. The

following subchapter discusses the impact of these factors on the amount of required

traffic channels and bandwidth.

of 64

4.2.2.1 Cell sizes

Average TETRA cells are remarkably larger than GSM cells. Firstly, TETRA uses

typically a frequency of 400MHz, while GSM uses 900 or 1800MHz. The propagation

losses are theoretically proportional to the square of the frequency [12]. Secondly,

commercial networks are typically capacity driven and PSS networks with less users

are coverage driven. This means that the population density usually determines cell

sizes in GSM.

The planned TETRA network in Germany consists of roughly 3000 cells [32]. In

contrast to that, the existing GSM network from Vodafone has 38100 cells using 15700

base stations [29]. Assuming that most of the base stations have either 1 or 3 cells, we

get 11200 three-cell base stations and 4500 one-cell base stations.

Overall we get an average relation of GSM:TETRA cells of 12.7:1. Due to the high

capacity requirements in densely populated areas, the relation is somewhat higher in

urban than in rural regions.

Taking into account the fact that there is a relatively high cell overlapping in the existing

GSM networks, it would be basically possible to use only part of the cells for group

calls. In urban areas, the network often consists of an overlay network providing

coverage over a large area and micro cells improving location probability and providing

capacity in densely populated areas. Building an overlay network by using only macro-

cells for the group calls significantly reduces network costs because not all base

stations need to be upgraded to support ASCI functionalities. Additionally we will see

later that it reduces the generated load in the network. The main drawback, however, is

a lower location probability which leads to a lower quality of service.

The table below shows the assumptions for the calculations in the next chapters. The

average cell sizes for the GSM overlay solution are assumed to be double compared to

the commercial GSM network.

TETRA GSM ASCI GSM ASCI overlay

Average cell area (km2) 120 10 20 Frequency re-use factor 19 12 12 Bandwidth per carrier (kHz) 25 200 200 Bandwidth per channel (kHz) 6.25 25 25 Table 2: Cell sizes and bandwidths

of 64

4.2.2.2 Traffic modelling of group calls

Models are commonly used to estimate the total traffic in a telecommunication system.

In commercial networks the input data are subscriber density, area coverage and busy

hour traffic per subscriber [16]. The call intervals as well as the call durations are

assumed to be exponentially distributed (so-called Poisson traffic). In this case, the

required amount of traffic channels can be determined by using the Erlang C-formula

which is shown below.

Group calls used in PSS networks, however, have some special characteristics:

• The amount of users is known which means that the user density is derived

from the total amount of subscribers and not vice versa as in commercial

networks.

• In contrast to commercial networks, traffic is assumed to be constant over a

longer period of time. The traffic growth is limited due to the constant amount of

users. Network capacity seldom needs to be added. Network expansions are

mainly for improving coverage.

• Semi-duplex group calls reserve one traffic channel one each site which is

activated during the group call. Therefore, a traffic model for group calls

typically includes the amount of cells activated in an average call. The

assumption is that if a cell generates traffic to other cells due to group calls, it

will also have to take traffic from other cells in the same proportion.

• The variance of the call intervals is higher and calls are of short duration since

communication is used for tactical operation. During incidents, the capacity is

significantly higher than during normal times, which leads to a burstier traffic

distribution than Poisson traffic. ETSI recommends evenly distributed call

durations and exponentially distributed call intervals for PSS traffic models [6].

In practice, however, Erlang C formula, assuming exponentially distributed call

durations and intervals, is commonly used [3].

Erlang C formula:

The Erlang C formula assumes a queuing system and determines the probability that a

call needs to wait longer than a certain queuing period. This probability is determined

by using the two formulas which are described below. Po describes the probability that

a call is delayed (i.e. it needs to queue for resources):

of 64

•

−

•+=

∑−

=

1

0 X!N!

N

X

XN

N

o ANANA

AP (1a)

N = Number of available communication channels

A = Traffic intensity in Erlangs (λ*H), where λ = call interval

H = Mean holding time (i.e. average call duration) in seconds

The value PT describes the probability for exceeding a certain queuing time T. This

probability is also called grade of service (GoS):

( )

•−

−

•==> HTAN

T ePPTWP 0)( (1b)

W = Call waiting time in a FIFO queue.

T = A given queuing period in seconds

A typical value in PSS networks is a probability of 5% that the queuing time exceeds 5

seconds.

The described GoS is correct for a single site. In order to get the probability that all

sites are included into a call after a certain waiting time, the value is depending on the

amount of sites in the group call. Assuming that PT is similar for all sites, we get the

total PT according to the following formula:

PT (total) = 1- (1- PT)n

n = Amount of sites in the group call

Because group calls include different amount of sites, this effect is usually neglected in

the calculations and only the site-specific GoS is calculated.

Generated traffic:

Taking into consideration the assumption above, the generated traffic per cell is:

A = U · λ · H · n (2)

U = Amount of users per site

λ = Busy hour call attempts per subscriber

of 64

H = Average call duration (λ · H = traffic per user)

n = Amount of cells included in a group call

In a similar way we can also define the traffic generated on a site by one single group:

A = λ · H · G (3)

G = Amount of active subscribers in the group

The amount of cells included in a group call is depending on the group size, the

location and the moving behaviour of the group members as well as the average cell

size. These parameters differ between the main user groups, police, fire brigades and

ambulances. Below a short description of their typical call behaviour.

Police:

In normal situations, the average group size for traffic police is about 50 and the

members are spread over the whole area or district. This group is used for informative

purposes.

During a mission, a group size is typically about 5 and the members are located in a

certain, smaller area. The moving behaviour but also the size may be very different

depending on the mission type.

Fire brigades & ambulance:

During a mission, the group size is between 5 and 20 members which are located in a

certain area. Members are typically moving only within small distances except when

going to or leaving from the place of interest.

The so-called user profile for traffic modelling uses a weighted average of the above-

described values between the user groups. The numbers below are based on traffic in

existing TETRA networks [20].

The amount of active sites per call describes the amount of sites where at least one

active subscriber is located. The numbers have been estimated using an even

distribution of the subscribers in one forth of the group area, because in case of an

incident, group members are typically located in a relatively small area.

of 64

TETRA GSM ASCI GSM ASCI overlay

Mobile originated traffic (mErl) 7.3 7.3 7.3 Group size (users) 10 10 10 Group call area (cells for 400 km2) 4 40 20 Active sites per call 2 6 5 Table 3: PSS user profile

4.2.2.3 Call set-up time and open channel

The call set-up time requirement for PSS users is 0.5s. Currently this is only achievable

with TETRA and transmission trunking can be used for channel allocation. In GSM it

would be basically possible to reduce the call set-up time to about 1s, but this would

require major changes in the core network software and topology. In practice this is for

economic reasons not feasible in commercial networks. Therefore in GSM a traffic

channel needs to be allocated for the whole duration of a communication (message

trunking). If the call intervals are not predictable at all, a channel needs to be activated

for a group all the time (open channel).

The amount of simultaneously active groups, which can be served per site, is

significantly higher when using transmission trunking. The table below has been

calculated using formulas (1) and (3) with a GoS of 5% for exceeding 5 seconds

queuing time and an average call duration of 12 seconds. For example, a 2-carrier

TETRA base station can serve about 8 times more groups than a single carrier GSM

base station even though both have the same amount of traffic channels.

Amount of served groups per site

1 2 3 4 5 6 71

614

24

34

45

57

0

10

2030

40

50

60

1 2 3 4 5 6 7

Available traffic channels

Open channelTransmission trunking

Figure 2: Transmission trunking versus open channel operation

of 64

4.2.2.4 Shifting area group call

The support of shifting area group calls has a significant effect on the amount of traffic

channels involved in a group call. Using the subscriber profile above, the amount of

traffic channels which needs to be allocated for a group call, would be 2 for TETRA and

6 for GSM ASCI in case shifting group call area is supported. However, if this feature is

not supported and high moving interest of the subscribers is assumed, all cells in the

group area need to be activated. This would be 4 for TETRA and 40 for GSM. Taking

into account that shifting area can only be realized for TETRA, the relation of channel

occupations for a group call between TETRA and GSM is 1:20 in this example.

Walke suggests in his report as a bypass solution that it may be possible that a group

call activates all cells where members are located plus the adjacent cells. It is obvious

that this solution could only be used for user groups with low moving interest or if

transmission trunking is supported. Otherwise, in case of message trunking, group

members may lose the communication to the group when moving to other sites during

the relatively long call duration. Additionally the small cell sizes in GSM increase the

probability for cell changes during a call.

4.2.2.5 Required capacity on the radio network

Since the cell sizes are very different for TETRA and GSM it is not representative to

observe the amount of used traffic channels. The required bandwidth or the amount of

transceivers is more representative. The bandwidth can be either expressed in terms of

radio channels or frequency.

The required bandwidth depends on the carrier capacity per site, the bandwidth per

channel and the frequency re-use factor R. If the amount of cells in the network is

smaller than the reuse-factor, then the amount of cells has to be used as R in the

formula below. With a given carrier capacity C per site, the needed bandwidth in the

network would be:

TETRA: B = C · 25 kHz · R

GSM: B = C · 200 kHz · R

We are considering two cases: A regional network with an area of 900 km2 and 400

users representing a medium size city with rural surroundings and a Germany-wide

network with an area of 357 021 km2 and 529 000 users. In both cases, the average

group call area is 400 km2 and a group consists of 10 members. The assumption is that

all users are active during busy hours. This might seem like an overestimation of the

of 64

traffic, however, we will see that the calculated capacity for TETRA in table 5 is even

slightly less than the recommendations for the Germany-wide network [32].

Since GSM does not support shifting area group calls, nor does it fulfil the required

group call setup times, open channels have to be used for some groups. The following

assumptions have been taken:

• One radio channel on each site belonging to the group call area will be

activated during a group communication.

• 25% of the groups use an open channel for the communication, which means

that a traffic channel is allocated all the time for the group.

• 75% of the groups use transmission trunking, which means that these groups

have to accept longer call set-up times.

• The additional load generated by the talking subscriber and by mobile

dispatchers has been neglected (see table 1 in section 4.1.3).

The channel holding time for quasi-transmission trunking has been neglected in both

cases, GSM and TETRA. The generated traffic and required capacities per cell has

been calculated using formulas 1 and 2 for groups using transmission trunking. The

selected grade of service (GoS) corresponds to a probability of less than 5% that the

channel queuing time would exceed 5s. In case of open channel, one Erlang is

required on each site within the group call area during busy hours.

Since GSM ASCI is built on top of an existing network, the additionally required

capacity has been determined. As reference, the Vodafone network has been taken,

which consists of 38100 cells and 93600 transceivers [29] and has in average 18 traffic

channels per cell. We assume that the capacity in the network is optimised on all sites,

which means that 18 traffic channels carry up to 14.1 Erlang traffic during busy hours at

the given GoS. This value has been added to the generated traffic through group

communication and the sum has been used to determine the required amount of traffic

channels. The traffic on the control channel has not been analysed and it has been

assumed that no additional control channels are required for GSM ASCI. The average

amount of carriers is a statistical value which therefore may be any decimal number. In

case of TETRA, each site has one control channel for signalling purposes.

of 64

Network size 900 km2 and 400 users

Technology TETRA GSM ASCI GSM ASCI overlay

Amount of cells 8 90 45 Average amount of users per cell

50 4.4 8.9

Trunked traffic per cell 0.73 0.96 0.97 Open channel traffic per cell 0 4.44 4.44 Total traffic per cell in Erl 0.73 5.41 5.42 Required traffic channels per cell (GoS = 5% at 5s)

3 7 7

Required amount of carriers per cell in average

1 0.875 0.875

Required amount of transceivers in total

8 79 40

Required bandwidth in carriers

8 11 11

Required bandwidth in kHz 200 2200 2200 Table 4: Required radio network capacity for a small network

In this example, the required bandwidth for TETRA is 11 times less than for GSM.

Interesting is that the traffic per cell and the bandwidth requirement are the same for

both GSM solutions. However, the amount of transceivers in case of the overlay

network solution is only half because of the double average cell size.

Network size 357021 km2 and 529000 users Technology TETRA GSM ASCI GSM ASCI

overlay Amount of cells 2976 35703 17852 Average amount of users per cell

177.8 14.8 29.6

Trunked traffic per cell 2.60 3.24 3.24 Open channel traffic per cell 0 14.82 14.82 Total traffic per cell in Erl 2.60 18.06 18.06 Required traffic channels per cell (GoS = 5% at 5s)

6 19 19

Required amount of carriers per cell in average

1.75 2.375 2.375

Required amount of transceivers in total

5208 84795 42399

Required bandwidth in carriers

34 29 29

Required bandwidth in kHz 850 5800 5800 Table 5: Required radio network capacity for a large network

of 64

It is clear that the amount of sites is inverse proportional to the cell size. Together with

the required bandwidth, this determines the total amount of transceivers in a network.

Therefore, a TETRA solution requires significantly less carriers than GSM, even when

regarding an overlay solution. The amount of transceivers does not only determine the

size of the base stations, but also the amount of required transmission lines between

base stations and exchanges or base station controllers. This value has therefore a

major impact on the operational costs of the network.

The ratio of required bandwidths GSM:TETRA is about 7:1 for the countrywide

network. The reason that this ratio is smaller than for the regional network comes from

the fact that GSM has a lower frequency reuse factor than TETRA and TETRA does

not need to reuse frequencies in the small network. For the GSM solutions, the size of

the chosen group call area and the user density are directly proportional to the required

bandwidth. In case of TETRA, however, the size of the group call area has no influence

to the capacity since shifting area can be used.

The graph below shows the required bandwidth in dependence of the average group

call area. Input data are the same as for the calculation of the countrywide network

above where 25% of the groups use open channel communication. For TETRA, the

required bandwidth is constant at 850 kHz for a constant amount of users. If the group

call area is 20 km2 or less, the required bandwidth for GSM is 600 kHz. For larger

areas, the required bandwidth grows more or less proportionally to the group call area

and reaches significantly higher values than TETRA.

Required bandwidth (kHz)

0

5000

10000

15000

20000

25000

30000

10 20 50 100 200 500 1000 2000

Average group call area (km2)

GSM ASCITETRA

Figure 3: Influence of group call area to bandwidth

of 64

As discussed earlier, the location of the groups is very seldom predictable and

therefore, smaller group call areas can have a major impact on the quality of service

perceived by the end users. For example, traffic police units move in very wide areas

and a restriction of the group call area is in practical situations not acceptable.

Therefore, a direct comparison between the two solutions is very difficult and one has

to keep in mind that a network supporting shifting group call area always offers better

quality of service since it is not realistic to use extremely large fixed group call areas.

For further discussions, especially economic considerations, a group call area of 400

km2 has been chosen.

It is obvious that keeping a channel open all the time wastes radio resources. The

graph below shows, how the bandwidth requirement grows in the GSM network when

groups are using open channel communication instead of transmission trunking. The

calculations assume a group call area of 400 km2. TETRA can offer fast call set-up

times even if transmission trunking is used and therefore the bandwidth requirement is

constant at 850 kHz. For GSM ASCI open channel communication has to be used for

groups where fast call setups are required. The required bandwidth grows nearly

linearly from 1.6 MHz, if all groups use transmission trunking, to 18 MHz, if all groups

use open channels.

Required bandwidth (kHz)

0

5000

10000

15000

20000

0% 20% 40% 60% 80% 100%

Groups using open channel communication

GSM ASCITETRA

Figure 4: Influence of open channel communication to bandwidth

For further discussions, we assume that 25% of the users require fast call set-ups and

therefore use open channel communication in GSM.

of 64

4.2.3 Network security

Network security is mainly important for organisations where the communication is

secret. The network should ensure that no one not belonging to the group is able to

listen to the communication but also that no one is able to disturb the communication. It

should also be impossible to follow a certain subscriber by tracing or recording the

signalling on the control channel.

4.2.3.1 Authentication

Authentication ensures that only mobiles with a valid key are able to use the network.

In TETRA, authentication is done during registration. The network rejects mobiles

which return a wrong authentication key. In GSM, authentication is done during call set-

up and may be omitted during fast call set-up. Listening members in a group call are

not authenticated in GSM ASCI since there is no uplink signalling during the call. This

means that every mobile which has the group ID programmed to its SIM card, is able to

listen to a group call. This is a high security threat for many PSS customers.

In TETRA networks it is possible that the mobile authenticates the network. This mutual

authentication enables the mobile to detect fake base stations, thus it will not register to

base stations not belonging to the network. Pseudo mutual authentication is also

possible by using dynamic authentication keys. In such a case it is not possible for a

fake network to authenticate a subscriber, since a new key is used for each

registration.

4.2.3.2 Air Interface Encryption (AIE)

AIE encrypts all signalling and call information on the radio path. Besides the speech, it

encrypts also the identities of the mobiles and the data messages on the control

channel. This means that it is not possible to trace a mobile, for example, by following

the signalling on the control channel. AIE is in use for both standards, GSM and

TETRA. The TETRA algorithm uses longer keys and is supposed to be more secure

than the one in GSM.

4.2.3.3 End-to-end encryption (e2ee)

E2ee encrypts speech and data between the end-points of the communication.

Encryption and decryption are done in the end-terminals. The network infrastructure

offers a transparent transport layer which is supported by both technologies. Dynamic

keys may be delivered to the terminals using SDS/SMS. Even though, e2ee completely

protects against eavesdropping, it cannot encrypt signalling information. E2ee encrypts

of 64

all information on the traffic channel but not on the control channel. Therefore e2ee has

to be used in combination with AIE.

4.2.4 Summary of comparison on technical level

The analysis has been split into three areas: Network functionalities, capacity and

security. Each of the areas will be summarized separately in order to keep high

transparency. Since not all the features have the same importance, different weighting-

factors have been used:

• Critical features: 2

• Default weight: 1

• Minor features: 0.5

The fulfilment of the requirements has been scored as follows:

• Completely fulfilled: 100%

• Minor functionality missing: 75%

• Major restrictions in functionality: 50%

• Only a bypass solution existing: 25%

• Feature not supported at all: 0%

Since the priorities of features are different for the various user groups, different

weighting and scoring could be applied. The chosen values are interpretations from the

related literature and practical experience. The different functionalities and features

(arguments) have been summarised in tables which all have the following structure:

Weight Technology 1

Technology 2

Technology 3

Argument A WA A1 A2 A3 Argument B WB B1 B2 B3 Argument C WC C1 C2 C3 Argument D WD D1 D2 D3 Normalised sum of weighted grades Grade1 Grade2 Grade3

The normalised sum of weighted grades (Grade1) has been determined according to

the following formula:

of 64

⋅

+⋅

+⋅

+⋅

⋅=

∑∑∑∑∑=====

3

1

13

1

13

1

13

1

11

1

yy

D

yy

C

yy

B

yy

AD

Axx D

DW

C

CW

B

BW

A

AW

WGrade (4)

Grade2 and Grade3 are calculated in a similar way.

Regarding the group call functionalities how they are perceived by end-user, GSM

ASCI lacks of major functionalities which may be crucial for PSS users. Most of the

missing features cannot be even compensated using proprietary features since they

are directly related to the air interface signalling. For example, speech item priorities

cannot be implemented unless specified by the standard.

Another major drawback of GSM ASCI is that no signalling is possible to listening

members in a group call. The long GSM ASCI call set-up times cause that open

channel communication has to be used for certain user groups. This means that

mobiles are not able to receive any individual calls or SDS as long as the group radio

channel is open.

Weight TETRA GSM ASCI GSM ASCI overlay

Group size limitations 1 100% 50% 50% DGNA 1 100% 25% 25% Group messaging (SDS) 0.5 100% 25% 25% Call priorities 2 100% 75% 75% Speech item priorities 2 100% 0% 0% Priority scanning 1 100% 0% 0% Late entry 1 100% 100% 100% Fast handover 1 75% 50% 50% Radio coverage 1 75% 75% 50% Direct mode 1 100% 0% 0% Base station fallback 1 100% 0% 0% Normalised sum of weighted grades 0.675 0.168 0.158 Table 6: Network functions

The long call set-up times and the non-existence of shifting area group calls have

major impact on the required air interface and core network capacity. Since GSM ASCI

has been first of all developed for railways, shifting area has not been a crucial

argument during the development of the standard. For PSS customers, where the

location of the users is not known in advance and cell changes must be possible,

shifting area is a critical requirement.

of 64

The row traffic channel usage takes into account that the speaking user as well as all

mobile dispatchers require an own traffic channel in GSM.


Cell size 0.5 100% 50% 75% Frequency reuse 1 50% 100% 100% Bandwidth per channel 1 100% 50% 50% Call set-up time 2 100% 25% 25% Shifting group call area 2 100% 25% 25% Traffic channel usage 0.5 100% 75% 75% Normalised sum of weighted grades 0.541 0.225 0.233 Table 7: Network capacity

Main drawback of GSM ASCI related to security is the fact that listening members in a

group call are not authenticated and authentication may be skipped or postponed if fast

call set-up is used. The importance of the security arguments differs very much

between the user groups. Rescue forces, like ambulance or fire brigades, typically do

not need 100% protection against eavesdropping, however, for police forces proper

authentication and encryption is a must.


Authentication 1 100% 50% 50% AIE 2 100% 50% 50% E2EE 0.5 100% 100% 100% Normalised sum of weighted grades 0.476 0.262 0.262 Table 8: Network security

In all three areas, GSM ASCI shows clearly lower performance than TETRA. The

summary of the technical analysis is a weighted sum of the discussed areas. Network

functions and security are weighted with 40% and network capacity with only 20%

since its influence is mainly on economic level, where it will be considered once more.


Network functions 40% 0.675 0.168 0.158 Network capacity 20% 0.541 0.225 0.233 Network security 40% 0.476 0.262 0.262 Normalised sum of weighted grades 0.569 0.217 0.214 Table 9: Summary of technical analysis

The graphical representation shows that the advantage of TETRA is similar in all three

areas, which means that using different weighting has hardly influence to the result of

the technical analysis.

of 64

Summary of technical analysis

TETRA GSM ASCI GSM ASCIoverlay

Prop

ortio

nal p

oint

sNetwork securityNetwork capacityNetwork functions

Figure 5: Summary of technical analysis

4.3 Economic analysis

The fact that the financing models for the two solutions in question are typically

different makes a direct comparison very difficult. Aim is to compare for both cases the

most cost-saving solution, for example, by using synergies with an existing network

infrastructure. The assumption is that an existing operator would operate the networks.

This opens the possibilities of using already existing sites and transmission equipment

for the implementation of the new network.

As far as possible, only group call related expenses are discussed, since the aim of the

study is to compare the cost impact of the group call functionalities. In many cases a

clear distinction is difficult, because the causes of the costs are not transparent and

often shared between different services.

A TETRA network needs to be built up from scratch. Existing network elements, for

example, from a GSM network, cannot be reused. However, transmission lines and

sites can be shared, if base stations and exchanges are co-located.

In case of a GSM ASCI network, there exist basically 3 possibilities:

1. Use completely the existing network by upgrading all network elements and

necessarily by adding capacity.

2. Build an overlay network by upgrading only part of the cells of an existing

network. This way, the amount of base stations to be upgraded could be

minimised.

of 64

3. Build an overlay network with new base stations on existing sites. In this

solution, the amount of sites supporting group calls would be the same as for

the second solution.

The two last approaches would have an impact on the offered radio coverage and thus

decrease the grade of service compared to the first option. The third solution requires

higher investment compared to the second solution. However, the advantage is that

traffic from PSS and private customers will not share the same resources. In this

sense, the third solution can be regarded as safer for mission critical tasks. The

operational expenses are supposed to be similar for the two last approaches, because

the amount of involved network elements is about the same. In the discussions below,

we will focus only on the first and second solution, as they are the most economic

alternatives.

In many cases it is planned that the state or an operator consortium makes the network

infrastructure investments. End user equipment like radio terminals and dispatcher

stations need to be paid by the user organisations which also pay a certain fee for

using the network.

For further comparison we assume the same Germany-wide network, as in the

technical analysis, with the following dimensions:

TETRA GSM ASCIGSM ASCI

overlay Bandwidth (kHz) 850 6400 6400 Transceivers 5208 93721 46862 Cells 2976 35703 17852 Base stations 2976 14693 5951 BSC none 400 400 Exchanges 34 160 160 Dispatchers 3000 3000 3000 Mobiles 529000 529000 529000 Table 10: Amount of network elements

The directly related costs for implementing the networks are included in the capital

costs, therefore the IMPEX are not discussed separately. All price levels are from non-

public sources and are only indicative. Aim of the pricing comparison is to show the

tendencies when using different configurations. Exact prices highly depend on

manufacturers and countries and have to be compared on a case-by-case basis.

of 64

4.3.1 CAPEX

Compared to a commercial network, a PSS network is typically built straight to the

required capacity. Once the network is running, the traffic growth is rather slow.

Therefore, most of the investments are needed in the beginning during the initial rollout

of the network. The overall investments consist mainly of the following items:

• Exchanges

• Base stations including antenna systems

• Radio terminals

• Dispatching stations

In most financing models, the network infrastructure and end-user terminals are paid

from different sources. Additionally the lifecycle of end-user equipment is much shorter

than of the infrastructure. Therefore, these two items are discussed separately.

4.3.1.1 Network infrastructure

Since a GSM based solution can be built from an existing network, most network

elements can be reused. However, since the ASCI features require modifications in all

exchanges and base stations, SW and possibly also HW upgrades are required. The

price of such an upgrade depends on the amount of development work and the size of

the target market. Of course it may also be part of the manufacturer’s strategic pricing;

therefore it is difficult to give a general estimation. The diagram below shows the price

of the infrastructure for the three solutions under the assumption that the GSM

networks do not require additional transceivers in order to carry the traffic caused by

the PSS customers. The higher the price for an upgrade is, the more expensive the

GSM solutions will be. We can see that even if an upgrade costs up to 25% of a new

element, the GSM solution is still cheaper. A typical relation between an upgrade and a

new element is about 1:10 or 10%. This value will be used in further calculations below.

At that level, a GSM network upgrade would be roughly 3 times cheaper than a new

TETRA network.

of 64

Infrastructure without additional transceivers (M€)

0.0

50.0

100.0

150.0

200.0

250.0

5% 10% 15% 20% 25%

Upgrade price in relation to new equipment

TETRAGSM ASCIGSM ASCI overlay

Figure 6: Infrastructure without capacity expansion

Earlier, in the technical comparison (figure 3), we have seen that the chosen group call

area has a major influence on the capacity requirement for a GSM solution. If additional

capacities are required, the GSM network needs to be equipped with new transceivers.

The diagram below shows the influence of the group call area on the total price of the

infrastructure under the assumption that the relation of the transceiver prices between

GSM and TETRA is about 1:4. The cost of possibly required additional MSC and BSC

is not taken into account.

Total cost of infrastructure (M€)

0.0

200.0

400.0

600.0

800.0

1000.0

10 20 50 100 200 500 1000 2000

Average group call area (km2)


Figure 7: Infrastructure costs in relation to group call area size

of 64

In the technical comparison we regarded 400 km2 as a typical group call area covering

a medium size city with its surroundings. In this case a GSM solution would be about

60% more expensive than a new TETRA network. The cheaper GSM overlay network

would cost about the same as TETRA. It can be clearly seen that the price of a GSM

network is determined mainly by the price of the transceivers, especially if large group

call areas have to be offered.

GSM reaches a breakeven with TETRA at a cell size of 210 km2 and for the overlay

network at 500 km2. For larger average cell sizes, the TETRA solution is becoming the

more economic solution regarding the CAPEX of the network infrastructure. 210 km2

corresponds to a cell radius of about 9 km. For most PSS users, the limitation of the

group call area to such a small size would cause high restrictions to their daily work

and would hardly be acceptable.

During the technical analysis, we have also compared the required bandwidth based

on the proportion of groups using open channel communication for GSM (figure 4).

This comparison can also be projected to the economic level. Assuming a group call

area of 400km2, we see in the graph below that the investment costs for a GSM ASCI

network are about the same as for a TETRA network if 10% of the groups require open

channel communication. The breakeven for an overlay network is at 35%. If more

groups have to use open channels, TETRA becomes the cheaper solution. The

following economic comparison assumes that 25% of the groups use open channels.

Total cost of infrastructure (M€)

0

200

400

600

800

1000

0% 20% 40% 60% 80% 100%

Groups using open channel communication


Figure 8: Infrastructure costs in relation to communication requirements

of 64

4.3.1.2 End-user equipment

The end-user equipments mainly consist of radio terminals and dispatcher stations.

Detailed pricing analysis seems to be very difficult since corresponding products do not

exists for GSM technology for the time being.

Radio terminals:

The mobile terminals are a significant cost factor and they stand typically for about half

of the total investment costs. However, since terminals are bought by the user

organisations and not by the operator, they are often not in the main focus of price

discussions when selecting a network technology. Both technologies, TETRA and

GSM, are standardized, which means that radio terminals can be bought separately

from different vendors. For example, for TETRA there exists a wide range of products

in different price classes. Since GSM ASCI terminals are not available at the moment

an exact comparison of the prices is not possible. Based on the results from the

literature review it can be assumed that there is no major price difference between

GSM ASCI and TETRA terminals.

It has to be understood that the price comparison refers to GSM terminals, supporting

ASCI features. The following features, which are supported by TETRA terminals, will

not be available in standard GSM ASCI terminals:

• Direct mode: Would require an additional receiver on the 400 MHz band.

• Scanning, fast handover or simultaneous SMS and Voice: Would require an

additional receiver on the GSM band.

• Packet data: Would require GPRS support (not directly related to group calls).

The mentioned restrictions are not taken into account at this stage of the analysis,

since they have been considered in the technical part. It seems, however, clear that

GSM terminals supporting also all above mentioned features would be significantly

more expensive than the currently available TETRA terminals. The cost impact of end-

to-end encryption is not considered here.

Dispatching stations:

Dispatching stations are typically connected via an application-programming interface

(API) to the network infrastructure. Such interfaces are available for both technologies.

We can assume that the development of dispatching SW will require about the same

amount of work for both solutions and therefore no major price difference is expected.

of 64

4.3.2 OPEX

When comparing the overall costs of a PSS networks, usually operational costs for a

time period of 10 or 15 years are considered. A possible OPEX impact of radio

terminals has not been taken into account.

4.3.2.1 Frequency licenses

As discussed in the technical part, the required bandwidth depends highly on the

average group call area. The technical comparison showed that TETRA requires

theoretically about 7 times less bandwidth compared to group calls based on GSM.

This value assumes that PSS and private users have the same GoS requirement. If

private users can accept lower GoS, the bandwidth for GSM could be reduced to some

extent.

For PSS networks, the price of the frequency licenses is usually not that relevant, since

the customer segment consists of state organisations and the frequencies are given to

the operator free of charge for that specific purpose.

4.3.2.2 Transmission

In mobile telecommunication networks, the transmission costs stand for about

30…40% of the discussed OPEX. In rural areas the price is typically somewhat higher

than in urban areas because of lower capacities. The costs are roughly proportional to

the amount of transceivers in the network and the required bandwidth per transceiver.

The relation between required transceivers is:

TETRA : GSM = 1 : 16

TETRA : GSM overlay = 1 : 8

The required bandwidth per GSM carrier is 2x64kbit/s plus some capacity for signalling

which has been neglected. In case of TETRA the value is manufacturer-specific and in

case of Nokia it is 64kbit/s per carrier. In case of GSM, it is only a question of adding

capacity to an existing network. Therefore the price for the transmission per bandwidth

can be expected to be somewhat cheaper. The table below assumes costs of 200€ per

64kbit/s per month and shows expected yearly OPEX.

of 64

TETRA GSM ASCI GSM ASCI

overlay Transceivers 5208 84795 42399 OPEX (M€) 12 407 204 Table 11: Transmission OPEX

In case of TETRA we can assume that the base stations and exchanges are co-located

with elements from existing networks like GSM. Therefore, also for a TETRA solution,

the transmission resources could be shared. Depending on the infrastructure

manufacturer, additional multiplexers may be required on the sites. These costs have

been considered when calculating the base station CAPEX.

4.3.2.3 Site costs

Site costs stand for a major part of the overall network OPEX; their impact is roughly

the same as from transmission. The site costs mainly consist of: energy consumption,

site rental for base stations and exchanges as well as rental costs for antenna mast

usage.

When upgrading a GSM network with ASCI features, no additional base stations,

antennas or exchanges are required. The only new elements are the GCR units and

additional transceivers in the base stations. Additional MSC and BSC are not

considered. Therefore the additional site costs, caused by upgrading a network for PSS

use, are minor.

Currently available TETRA base stations are significantly larger than GSM units, which

result in higher rental costs per base station. Because of the lower frequency band,

also the antennas are larger compared to GSM. The table below assumes base station

and exchange site costs of 500€ per month and shows the expected yearly OPEX.

TETRA GSM ASCIGSM ASCI

overlay Base stations 2976 14693 5951 Exchanges 34 160 160 OPEX (M€) 18 < 1 < 1 Table 12: Site OPEX

4.3.2.4 Operation and maintenance

Regarding the technical network management, a shared GSM network does not cause

significant additional costs if ASCI features are introduced and capacity is added. A

TETRA network, however, would require a new network management system with

of 64

partly dedicated technical personnel. Large networks are typically managed in a

centralized way and modern network management centres allow the simultaneous

control of several network types.

Detailed figures depend also very much on the operational model of the operator. It can

be assumed that the management of the shared GSM network would be slightly

cheaper than an independent TETRA network.

Regarding SW and HW changes it is clear that upgrade costs in a GSM network are

significantly higher than in a comparable TETRA network since the network element

volumes are much larger. In order to get a fair picture, the upgrade costs for the GSM

network have to be distributed according to the user segments: PSS and commercial

users. The applied cost distribution will highly affect the relative upgrade price of the

PSS part of the network. Because of the missing transparency, upgrade prices for the

two solutions are regarded to be on a similar level.

4.3.3 Risks

The target date for implementing the PSS network in Germany is the year 2006 which

is 3 years from now. The rollout is planned to start in 2005. Estimating the economic

impact of technical risks includes the probability that the technical solution is available

in time. The second factor is the amount of caused losses, in case the solution is not

available or delayed. Per definition we have:

Cost of risk (risk premium) = Probability of an incident · Cost of the incident

For example, if the probability of the occurrence is 15% and the possible losses are

400€, then the risk premium to be taken into account would be 60€.

4.3.3.1 Network infrastructure

GSM ASCI features have been developed since about 4 years and a demonstration of

the usability for PSS users is currently ongoing in Würzburg, Germany [30]. At that

moment it is impossible to say at what time countrywide services could be

demonstrated on the GSM ASCI technology. Since the functionality is based on an

existing network, the countrywide availability of the service should not be a problem.

The risk might be rather that the services do not cover the end-user expectations.

Major TETRA manufacturers have been developing TETRA networks for the last 10

years and the first network with countrywide services is in operation since 2002.

of 64

When disregarding the restrictions of the GSM network as discussed in the technical

analysis, it is very likely that both technologies are available in 2006.

4.3.3.2 Mobile terminals

The economic risk related to mobile terminals is much higher than for the network

infrastructure. The reason for this is that if the network needs to be upgraded because

of misbehaviour or a missing requirement, it can be done in a centralized and properly

timed way. But in case non-mature terminals have been distributed to the end-users,

they all need to be collected and re-programmed one by one.

If we assume a 25% probability that the mobiles need to be reprogrammed, after they

have been distributed to the customers, because of technical problems, the resulting

risk premium at reprogramming costs of 100€ per terminal would be:

25% · 100€ · 529000 = 13.2 M€

At this moment, TETRA terminals are available from different manufacturers. GSM

ASCI terminals exist only as prototypes and they are not available on the market.

Furthermore, the user interface for GSM ASCI terminals has not yet been optimised for

PSS users, as it can be seen from related product presentations [28]. The development

of mature mobile terminal products takes typically at least 1…2 years. In this sense it is

very unlikely that corresponding products are available in 2006.

Currently non-existing functions for GSM ASCI like, for example, direct mode or priority

scanning would require additional development work which has not been considered

here. Also cost effects for the end-customers due to delayed deliveries have been

neglected.

4.3.3.3 Dispatching stations

Since the APIs towards TETRA and GSM infrastructure are similar, no major

differences in the risks are expected. Today, ready-made dispatching stations for

various user groups exist for TETRA technology. For GSM, dispatching stations are

available for the railway-segment.

Typical requirement is that the new user interface needs to be adjusted for the existing

control-room infrastructure of the respective PSS organisation. Therefore, some new

development work is required in both cases and related risks can be estimated to be

similar.

of 64

4.3.4 Summary of comparison on economic level

The different results have been combined as a weighted sum using formula 4 which is

described in section 4.2.4. The weighting has been done similarly as for the technical

comparison:

• Critical features: 2

• Default weight: 1

• Minor features: 0.5

Because the costs and risks cannot be compared directly, a proportional scale has

been used also in this case. The described costs are all estimates which depend on a

high number of factors and can therefore vary extremely much. The aim of this study is

to show the impact and tendencies of different factors in a transparent way. Therefore,

the OPEX and CAPEX have not been summed up as absolute values as this would be

done when estimating the overall costs of a real network. The OPEX and CAPEX have

been scored as follows:

• Most economic solution: 100%

• (Cost of most economic solution / Cost of compared solution) in percent

Since an exact risk estimate is impossible, the following scoring has been applied to

reflect different risk levels. The interpretations of these values may highly differ, for

example, between various manufacturers and users groups:

• No risk, solution is existing: 100%

• Solution not existing but most probably available in time: 75%

• Minor delays and need for corrections to be expected: 50%

• Major delays and need for corrections to be expected: 25%

On the CAPEX side, there are only differences in the network infrastructure. The higher

costs for the GSM network is mainly based on the additional transceiver units which

are required to fulfil the capacity needs, calculated in the technical analysis.

of 64

Weight TETRA GSM ASCI GSM ASCI

overlay

Network infrastructure 1 86% 58% 100% End-user equipment 1 100% 100% 100% Normalised sum of weighted grades 0.343 0.286 0.371 Table 13: CAPEX

Main contribution to OPEX are caused by transmission and site costs and therefore

they are weighted accordingly strong. Transmission costs are once more proportional

to the capacity, which causes additional costs for the GSM solutions. Regarding the

site costs, however, GSM is supposed to be the more economic solution, since there

are hardly any new sites required.


Frequency licenses 0.5 100% 15% 15% Transmission 2 100% 3% 6% Site costs 2 5% 100% 100% O & M 1 75% 100% 100% Normalised sum of weighted grades 0.462 0.264 0.274 Table 14: OPEX

The availability of GSM ASCI terminals which fulfil the PSS user-requirements forms

the highest risk factor and has major impact to the risk estimation for the GSM

solutions.


Network infrastructure 1 100% 75% 75% Mobile terminals 2 100% 25% 25% Dispatching stations 1 75% 75% 75% Normalised sum of weighted grades 0.517 0.242 0.242 Table 15: Risks

For the combination of the results, CAPEX and OPEX have been weighted similarly,

which reflects to the NPV of a period of 5…10 years. For longer periods, OPEX

become more significant. CAPEX and OPEX have been weighted with 40%. The

economic impact of the risks is supposed to be somewhat less and therefore the

weight is only 20%.

of 64

Weight TETRA GSM ASCI GSM ASCI

overlay CAPEX 40% 0.343 0.286 0.371 OPEX 40% 0.462 0.264 0.274 Risks 20% 0.517 0.242 0.242 Normalised sum of weighted grades 0.425 0.268 0.307 Table 16: Economic analysis

Even though the GSM solutions can utilise existing infrastructure, they appear to be

more costly than a TETRA solution. Main reason is the additional capacity which is

required in the network based on an average group call area of 400 km2. The smaller

the required group call area, the lower would be the capacity requirement for GSM.

Note that the graph shows the favourability of a solution: The lower the costs are the

more points are given and vice versa.

Summary of economic analysis


Prop

ortio

nal p

oint

s

RisksOPEXCAPEX

Figure 9: Economic analysis

In order to estimate the overall costs of the network, the absolute costs should be used

instead of the weighted grades. The chosen approach gives in this sense a generic

result and the impact of the different areas should be analysed in more detail if

necessary.

GSM without capacity expansion:

Let’s consider the case that the GSM implementation would not require additional

capacities to the network for serving the PSS customers. In this case, the costs for the

network infrastructure have earlier been estimated to be about one third of what a

TETRA network would cost (figure 6). The investments would consist only of the

of 64

upgrade costs and the new elements like GCR. The weighting of the different areas is

similar as above.


Network infrastructure 1 32% 80% 100% End-user equipment 1 100% 100% 100% Normalised sum of weighted grades 0.242 0.355 0.403 Table 17: CAPEX

There are hardly any additional OPEX, because most of the costs are strongly related

to the added network capacity which is zero in this case. Frequency licenses are

proportional to the additional bandwidth, transmission costs to the amount of

transceivers and site costs to the amount of base stations and exchanges. As a result

we get a significantly better performance for GSM compared to TETRA.


Frequency licenses 0.5 0% 100% 100% Transmission 2 0% 100% 100% Site costs 2 5% 100% 100% O & M 1 75% 100% 100% Normalised sum of weighted grades 0.058 0.471 0.471 Table 18: OPEX

The risk estimations do not differ compared to the first case where additional capacities

are considered. The results have been combined in a same way as for the previous

scenario.


CAPEX 40% 0.242 0.355 0.403 OPEX 40% 0.058 0.471 0.471 Risks 20% 0.517 0.242 0.242 Normalised sum of weighted grades 0.224 0.379 0.398 Table 19: Economic analysis

In this case there are considerable advantages for the GSM solutions, especially on the

OPEX side. It has to be kept in mind that this scenario is not realistic and should be

only used for illustrating the cost effect of the capacity requirement.

of 64

Economic analysis (no added capacity)


Prop

ortio

nal p

oint

sRisksOPEXCAPEX

Figure 10: Economic analysis

4.4 Combination of the results

There are no general rules whether the technical or economic arguments weight more

in such a comparison. In a commercial network, low technical performance may lead to

losing customers and thus inefficient usage of the network. In a PSS network, the users

are dedicated to the network since there are no competing services available. On the

other hand their requirements are more critical as they are needed for fulfilling the

user’s tasks. This means that the technical arguments are not directly linked to the

economic performance of the network, but they are important arguments for selecting a

technology. In the table below, the results from the technical and from the economic

analysis have been weighted similarly strong.

Network functions Weight TETRA GSM ASCI GSM ASCI

overlay Technical comparison 50% 0.569 0.217 0.214 Economic comparison 50% 0.425 0.268 0.307 Normalised sum of weighted grades 0.497 0.243 0.260 Table 20: Overall result

The graphical representation illustrates the clearly stronger performance of TETRA.

There is only a marginal difference between the two GSM solutions in favour of the

overlay network which is based mainly on the lower amount of required network

elements. Technically the overlay network has slightly lower performance.

of 64

Overall results


Prop

ortio

nal p

oint

sEconomicalTechnical

Figure 11: Overall result

GSM without capacity expansion:

Regarding the scenario that no additional capacity is required for the GSM networks,

we can observe clearly improved performance for these solutions. However, they are

not able to compensate the low scoring from the technical comparison. Also in this

case the overlay network ends up with a slightly better result than the normal GSM

network.

Network functions Weight TETRA GSM ASCI GSM ASCI

overlay Technical comparison 50% 0.569 0.217 0.214 Economic comparison 50% 0.224 0.379 0.398 Normalised sum of weighted grades 0.396 0.298 0.306 Table 21: Overall result without capacity expansion

This scenario can only be realistic, if the average group call area is so small that it

would not require additional carriers on the base-station sites. According to the

calculations in the technical part, even for group call areas smaller than 20 km2 at least

2 traffic channels are required in order to carry the group traffic. This means that we

can use a GSM network without capacity expansion only if the group call area is

geographically very limited. It is unlikely that mission critical PSS users can accept

such a restriction. One possibility to guarantee the required service level for PSS users

would be to reduce the GoS for private users, but this is hardly reasonable in a

commercial network.

of 64

Overall results (no added capacity)


Prop

ortio

nal p

oint

sEconomicalTechnical

Figure 12: Overall result without capacity expansion

4.5 Sensitivity analysis

This section discusses which parameters could directly affect the overall result. The

arguments have been mentioned earlier, and the aim at this point is to review the most

critical factors.

Compared to other existing studies, this technical analysis uses weights for different

functionalities in order to reflect their importance. A stronger influence to the end-result,

however, has the fact that features, which are not related to group calls, have been out

of scope. Since TETRA is especially designed for group calls, its main advantages are

in this area. Hence, if other functionalities like individual calls had been included, the

technical advantages of TETRA would not have been that significant.

The economic analysis is very much driven by capacity requirements for the

countrywide network. The following assumptions have major impact on the required

capacity:

• All 529 000 radio subscribers are supposed to be active during busy hours

• 25% of the groups in GSM use open channel communication

• The average group call area is 400 km2

The less the required capacity is, the more economic a GSM solution gets. In this

sense, the comparison with a GSM network without capacity expansion, done in the

previous section, gives precious information for comparing the end-results.

of 64

Whether technical or economic arguments count more is highly driven by political

factors and also by the current market situation. Additionally the cost of risks is very

difficult to estimate and the chosen values reflect the current technological status.

4.6 Conclusions

This study has compared group call functionalities based on the GSM and TETRA

technology. It points out how the technologies fulfil the user requirements and how

economic they are for a countrywide network solution. The ETSI standard TETRA

appears to show stronger performance than a comparable GSM solution in nearly all

areas. The main reason can be found in the technical maturity of the solution, but also

in the capacity requirements which are based on TETRA’s:

• Low bandwidth

• Large cells

• Shifting area group call

• Fast call set-up times

Shifting group calls and fast call set-up times are theoretically also achievable for GSM

ASCI, but they would require major changes in the core network architecture. For

economic reasons it is very unlikely that these changes will be implemented in

commercial GSM networks.

The GSM group call functionality can, therefore, only be competitive for user groups

where the group call area is clearly defined or where group members have very low

moving interest. This is, for example, the case for railways, where GSM already today

has a remarkable market share. TETRA, however, is the only reasonable solution if the

moving behaviour of the users is unpredictable. It fulfils all major technical

requirements at a competitive cost level.

It has to be understood that this study does not make a complete comparison between

the technologies. Only group call functionalities have been observed and other

requirements, like individual speech- and data-calls, have been outside the scope.

Taking into account that in PSS networks about 80% of the traffic is caused by group

communication, the results of the study allow a relevant statement about the suitability

of mainstream technologies for this segment. High- quality group call functionalities are

a must for future PSS networks and form the most important criteria, when comparing

different technologies.

of 64

4.7 Future prospects

The fast technical development in the commercial networks makes it very likely that

mainstream technologies will be considered more and more for PSS networks. The

economic potential of technical synergies can help to achieve remarkable savings, but

still allows for the development of technically suitable solutions. TETRA MoU has

published a related study, focusing on the usability of UMTS for the PSS segment [24].

Their conclusion is that, even in the future, specialised technologies like TETRA will

survive. The main reasons are security arguments, since dedicated networks always

offer a better quality of service for mission- critical users than shared networks.

Additionally, technical requirements most probably weigh stronger than economic

arguments when choosing a solution for this segment.

It is important to understand that group calls are not just point to multi-point

communications. The discussed impact of group calls to the network capacity is also

valid for 3rd generation mobile networks. It is very unlikely that they are able to fulfil the

required fast group call set-up times or support shifting group call areas in the future.

For economic reasons it is not interesting for operators and network providers to offer

these kinds of services based on existing networks. Compared to a dedicated solution,

the amount of network elements is much higher in a commercial network, which makes

potential upgrades very expensive and risky. Solutions purely based on mainstream

technologies will be able to attract customer groups with lower quality of service

requirements. GSM-R is a good example for the implementation of group calls for the

railway segment. In the future, the so-called push-to-talk over cellular (PoC) is

supposed to gain market shares in the professional cellular segment like transport

companies, hotels or even private users, also. These technologies are able to provide

very basic group call functionalities at a very competitive price level, since the

modifications to the core network are relatively small.

However, for the mission- critical PSS segment, there will still be a demand for

dedicated networks with specialised functionalities. It remains to be seen whether the

PSS market is large enough for telecommunication equipment manufacturers to focus

on a specific solution. The tendencies during the last years have shown that most

probably only a few infrastructure and mobile manufacturers will remain. In order to

keep the market size as large and homogeneous as possible, it is very likely that

several manufacturers will choose the same technologies for their solution. Whether in

the future this will be a standardized solution or a de-facto standard is difficult to

estimate for the time being.

of 64

5. LIST OF REFERENCES

[1] Accenture Denmark; Rapport om radiokommunikation for beredskabet, version 1; 2003

[2] Danish ministries, Indenrigs- og Sundhedsministeriet, Finansministeriet, Forsvarsministeriet, Justitsministeriet, Ministeriet for Videnskab, Teknologi og Udvikling; Rapport om radiokommunikation for beredskabet; 2003

[3] Detecon, Motorola, Nokia, T-Systems; Planungsrichtilinie für das TETRA BOS Netz; 2002; (not publicly available)

[4] ETSI EN 300 392-2 V2.3.2; Terrestrial Trunked Radio (TETRA); Voice plus Data (V+D); Part 2: Air Interface (AI); 2001

[5] ETSI EN 301 419-3 V5.0.2; Digital cellular telecommunications system (Phase 2+); Attachment requirements for Global System for Mobile communications (GSM); Advanced Speech Call Items (ASCI); 1999

[6] ETSI ETR 300-2; Trans-European Trunked Radio (TETRA); Voice plus Data (V+D); Designer’s guide; Part 2 Radio channels, network protocols and service performance; 1997

[7] ETSI TS 100 932 V6.1.0; Digital cellular telecommunications system (Phase 2+); Enhanced Multi-Level Precedence and Pre-emption Service (EMLPP); 2000

[8] ETSI TS 100 933 V8.2.0; Digital cellular telecommunications system (Phase 2+); Voice Group Call Service (VGCS); 2000

[9] ETSI TS 100 934 V8.2.0; Digital cellular telecommunications system (Phase 2+); Voice Broadcast Service (VBS); 2000

[10] ETSI TS 143 068 V5.2.0; Digital cellular telecommunications system (Phase 2+); Voice Group Call Service (VGCS); 2002

[11] ETSI TS 143 069 V5.2.0; Digital cellular telecommunications system (Phase 2+); Voice Broadcast Service (VBS); 2002

[12] ETSI TR 101 362 V7.1.0; Technical Report; GSM Radio network planning aspects; 2000

[13] Gartner, Basso M.; New Mobile Network Enhances Public Safety in Finland; Case Studies, CS-20-2732; 2003

[14] Gartner, Chapman Jason; Europe's Standard Shows Way Forward for Private Mobile Radio; 2003

[15] Gartner; Uavhengig vurdering av konklusjoner i rapporten “Konvergering av trådløse nett”; 2002; http://www.odin.dep.no/archive/nhdbilder/01/06/NHDTe071.pdf

[16] Jakes William C.; Microwave Mobile Communications; Wiley; 1974

[17] Morane PMT, Marconi; ASCI Features summary of performance tests on the morane trial sites; 2000; http://nedra.uic.asso.fr/docs/a43t00032.pdf

of 64

[18] Nexia and Preview; Konvergering av trådløse nett, Forstudie for Nærings- og Handelsdepartementet; 2002; http://www.odin.dep.no/archive/nhdvedlegg/01/03/Konve041.pdf

[19] Nokia; Evaluation of GSM, GSM ASCI (Advanced Speech Call Item), GSM-R AND UMTS compatibility to public safety communications requirements, white paper; 2002

[20] Nokia TETRA System Network Dimensioning and Radio Coverage Guide for Release 3.0, 2003 (not publicly available)

[21] Rollén Berit; Ett nät för trygghet, Rapport från Uppdrag Tetra radiokommunikation; 2002; http://www.sou.gov.se/rakel/PDF/Uppdrag_Tetra.pdf

[22] Smye Nick; The Use of Commercial Cellular Mobile Networks as a Solution for Public Safety Users in Norway; 2002; http://www.odin.dep.no/archive/nhdbilder/01/06/GSMfo052.pdf

[23] TETRA MoU, Information on Internet; 2003; http://www.tetramou.com/Tech/index.asp

[24] TETRA MoU Association; TETRA or UMTS – let the user decide; 2001

[25] Tetrapol Forum, TETRAPOL Specification: Radio Air Interface PAS 0001-2; 1998

[26] Tetrapol, Information on Internet homepage; 2003; http://www.tetrapol.com/www/tuc/references.php

[27] Trick Michael A.; Multiple Criteria Decision Making for Consultants; 1996 http://mat.gsia.cmu.edu/mstc/multiple/multiple.html

[28] Vodafone, Holzer Harald; Technische Realisierung der BOS Lösung; 2002; http://www.vodafone.de/downloadarea/Technische%20Realisierung.pdf

[29] Vodafone, Doppelfeld-Watson Jill; Betriebskonzept für BOS; 2002 http://www.vodafone.de/downloadarea/Betriebskonzept.pdf

[30] Vodafone, Press release: Vodafone D2 startet Live-Demo von GSM-BOS in Würzburg, 12.9.2003; http://www.vodafone.de/bos

[31] Walke Bernhard; Gutachten zur Einigung das um ASCI und Zusatzfunktionen erweiterten Vodafone D2 GSM-Mobilfunknetzes zur Erbringung der Dienste für das Digitalfunknetz der Behörden und Organisationen mit Sicherheitsaufgaben (BOS); 2003; http://www.vodafone.de/bos

[32] ZAN, Zentralstelle Digitalfunk; Digitalfunknetz für die Behörden und Organisationen mit Sicherheitsaufgaben (BOS); Abschlussbericht der Expertengruppe aus Bund und Ländern Gruppe „Anforderungen an das Netz“ (GAN); 2002

CORRIGENDA

A misinterpretation of the specifications lead to the wrong conclusion that group

scanning would not be possible with GSM ASCI. In fact, scanning and priority scanning

are possible for both technologies TETRA and GSM. Accordingly, the related

statements on pages 19, 29, 49 and 53 are not correct.

This has also minor impact to the tables comparing the technologies. The corrected

tables are show below:


Group size limitations 1 100% 50% 50% DGNA 1 100% 25% 25% Group messaging (SDS) 0.5 100% 25% 25% Call priorities 2 100% 75% 75% Speech item priorities 2 100% 0% 0% Priority scanning 1 100% 100% 100% Late entry 1 100% 100% 100% Fast handover 1 75% 50% 50% Radio coverage 1 75% 75% 50% Direct mode 1 100% 0% 0% Base station fallback 1 100% 0% 0% Normalised sum of weighted grades 0.622 0.194 0.184 Table 6: Network functions


Network functions 40% 0.622 0.194 0.184 Network capacity 20% 0.541 0.225 0.233 Network security 40% 0.476 0.262 0.262 Normalised sum of weighted grades 0.547 0.228 0.225 Table 9: Summary of technical analysis


Technical comparison 50% 0.547 0.228 0.225 Economic comparison 50% 0.425 0.268 0.307 Normalised sum of weighted grades 0.486 0.248 0.266 Table 20: Overall result


Technical comparison 50% 0.547 0.228 0.225 Economic comparison 50% 0.224 0.379 0.398 Normalised sum of weighted grades 0.385 0.303 0.311 Table 21: Overall result without capacity expansion

Helsinki, March 25, 2004

Simon Riesen

simon riesen the usage of mainstream technologies for public

Documents